I have talked to and read dozens of republicans about this and I've yet to meet one who mentioned Ron Paul voters (or, for that matter, Gary Johnson).
I don't think anyone will believe this was a factor - I doubt people will even think about it - except some of you here.
Reasons:
1 - The numbers don't even come close. Even a 51%-48% Romney win in the popular vote wouldn't be enough to win the election. The tipping state is Colorado that he'll lost by almost five points.
2 - There is a huge credibility problem. Romney didn't lose because he ostracised you. Most of you would never vote for Romney - or any other Republican except Ron Paul - regardless of what Romney had done: just read this forum. This is just a pretext.
3 - This is hugely important: Romney over-performed the "liberty candidates", candidates endorsed by Ron Paul and candidates endorsed by Rand Paul. Bentivolio and Amash. The down ticket candidates in New Hampshire (that were decimated). Those Senate candidates that Ron Paul endorsed like Connie Mack and Denny Rehberg. He did better than Rehberg by 14 points. Better than Flake by 7 points. Better than Mack by 13 points.
Rand Paul cut robocalls and spent money helping Mourdock and Akin. Romney over-performed them by gigantic margins. And Kurt Bills lost his race by 35 points - while Romney lost MN by 7 points. You can do the math.
What people are thinking when they look at the results is that candidates to the right of Romney did even worse. And at least in swing states, they did. Ron Paul endorsements proved to be worth very little - which is not surprising to me as I've been reading this site lately.
In the end, most hardcore Ron Paul supporters (his soft supporters voted Romney) and Libertarians will never vote for a GOP candidate, regardless of who that is (I'd comfortably include Rand Paul in here). The later are just sectaries - I was just checking results and they run a candidate against Amash who got 3% of the vote!! Not even Amash is good enough for them. That's just the "Chirping Sectary" vote. Most Ron Paul hardcore supporters are a bit like that too or they simply don't have any solid affinity with conservatism in terms of ideology and happen to support Ron Paul because they like his positions on foreign policy and mistake his position on fiat currency and his attacks on rent-seeking with the typical economic populism.
So there's basically no reason to go after those voters when not only they'd refuse to reach any type of compromise, it'd imply losing much more voters in the middle. The trade-off just isn't worth it.
You're correct that endorsements mean nothing to our voting in most cases (except to draw attention to candidates we might like), no matter who makes them. However, it's not because we'll only vote for one man. It's because we judge candidates based on who they are, and we consider endorsements and obedience to be of little to no value in and of themselves. You're looking at this through conservative blinders without a proper understanding of our diversity: Do we have people with a more populist economic sense than conservatives in your mold? Sure...but our core is full of staunch paleoconservatives and hardcore libertarians with a much deeper sense of economics and what a free market means than anyone that today's "conservatives" call conservative.
Did Romney lose Colorado by 5 points? Sure. Is that more than Ron Paul primary votes can account for? Sure. However, what you're missing regarding your first point is that a truly anti-war, anti-police-state Presidential candidate carries a great deal of crossover appeal to a lot of independents and Democrats who would otherwise vote straight D (as they did in this election). A lot of vocal liberals hate Ron Paul (etc.) and others wouldn't bother voting for him in a Republican primary (ew, yucky), but candidates with Paul's views resonate a lot more deeply with the younger liberal crowd than candidates with Romney's views.
What you're missing with your second point is that we DO, and WILL, vote for other people like Ron Paul. We've voted Amash, Bentivolio, Massie, Rand, etc. into Congress and the Senate, many voted for Cruz, we tried for Kurt Bills, and I voted for Gary Johnson last night (along with other candidates for other positions). You see all the kneejerk reactions to Rand Paul talking like a politician, which hits emotional sore spots after Ron Paul's boldness, but if you really think we're totally unsatisfiable, I think you've misjudged. There are four years between now and 2016.
We wouldn't have ever voted for Romney, no...and that's why the Republicans truly lost the Presidency not when Romney failed to woo us, but when they nominated him in the first place. You can blame whatever you want for Romney's failure, but do not overlook the fact that we TOLD you this would happen, and we told you he was unelectable. A Republican Bush with a different face was unelectable in 2008 and in 2012. We also wouldn't ever vote for the neoconservative candidates that ordinary Republicans consider "more conservative" than Romney, like Paul Ryan, or Chris Christie, or Marco Rubio. For those of us who view conservatism positively, they are not conservative to us...and for those of us with different identity politics, they're even more unacceptable. Even Flake doesn't inspire us, but it's not because we'll never vote for Republicans other than Ron Paul. It's because we have a different idea of respectable conservatism than people who have been taking their marching orders from Fox News and talk radio.
For most of us, the critical dividing issues between acceptable and unacceptable Republican candidates are generally
foreign policy and the police state (and we can also tell the difference between a free market candidate and a corporatist candidate who only pays lip service to the ideals of free enterprise). Foreign policy is a priority to us...and it's obviously a priority to the Republican leadership, considering it's the primary issue they refuse to compromise on (I mean, look at how much the Republicans have been huge spenders). The reason for this, of course, is because conservatives have unconsciously allowed themselves to absorb the views of Lieberman liberal Rupert Murdoch. We will never vote for a Republican who supports a neoconservative foreign policy, so no, the Republican Party cannot capture out vote by trying to churn out another neoconservative puppet. However, they also cannot win the Presidency without us anymore, which will become more true every year as the baby boomers fade and the younger generations rise. The time for empire is over, which is why the Republican Party cannot win the Presidency anymore until they allow someone to win the nomination who has a different foreign policy. That's what it comes down to: It's not about Ron Paul the man. It's about respect for the Constitution, and not supporting eternal war. Those are the concessions the Republican Party must make to capture the vast majority of our voting bloc.
On your third point, Congressional races can be different from Presidential races for a number of reasons. First, the crossover appeal to independents and Democrats is much greater in a Presidential election, due to the President's foreign policy role. Second, look not only at how much better the well-funded Romney performed than underfunded Congressional liberty candidates, but how much better he performed with the underfunded Congressional neoconservative candidates in similar districts (of course, bias in funding is going to limit your comparison pool). I don't have the numbers for you, but I can tell you that it would be a much fairer analysis.
You have to look at the demographics here: Neoconservative foreign policy is not the future. Federal social conservatism and disrespect for civil liberties is not the future. Today's younger generations are DRASTICALLY divided regarding our economic outlooks, but the Republican Party's most extreme foreign policy and social views totally alienate the vast majority of entire generations. The current Republican base cannot see this, because they're so homogeneous, being comprised mainly of middle/upper-middle class baby boomers and their families. They're vehemently defensive of their social traditions, scared of change, and so scared of changes in the world that they overreact to threats (War on Terror)...and it is primarily stubbornness on THESE issues, not on economic issues, that has catalyzed so much attrition to the Democrats. Of course, Obama's foreign policy isn't really any better than Bush's, but his rhetoric is marginally better, so the gradient is in his favor.
Without a Republican Party that even remotely speaks to younger generations on issues we consider so "obvious," the Democrats have captured our attention to a huge degree and indoctrinated many of us on more complex economic issues...and Obamabots are the result. The Republican's replacement of actual fiscal conservatism and free market principles with huge spending and corporatism has made this so much easier as well: America's youth are more keenly aware of our economic decline than older generations on average, and we know it started long before Obama. Without a champion of true free market values to set us straight, we have learned to associate Republican economic policies with decline, and too many have fallen into the waiting arms of socialism in search of a solution. Ron Paul has done a LOT to reverse this process, but the longer the Republicans remain obstinate on foreign policy and refuse to hand us the reins, the faster they will fade into complete irrelevance (to the economic doom of us all, I might add).