1) All vice presidents still have "ceremonial" offices in the Senate. Lyndon Johnson (maybe Hubert Humphrey) was the last one to really use it in a meaningful way (Agnew may have tried)--and having been Majority Leader, Johnson KNEW how to use it.
2) The problem with the Rand VP option is several-fold:
a) it would implicitly require Ron to endorse Romney, instead of keeping his mouth shut, or endorsing Johnson. If he does that, does he lose credibility with his supporters, who then say "oh, so it was just about politics, not really about making change"?
b) Rand could be shut out of decisionmaking just like Truman was (assuming a Romney win)--not even knowing that we had an atomic bomb or how WWII was being waged, or what discussions had been had with Churchill and Stalin....
c)if Romney loses, then Rand is in the position of having been part of that losing ticket. I didn't do a comprehensive historical search, and I may have missed someone, but I can only find one example, from either party, in the last 100+ years where a VP candidate on a losing ticket has later gotten his party's Presidential nomination...Bob Dole, who was the VP candidate in 1976 for Ford, and who (20 years later!) got the presidential nomination in '96(but of course didn't win). That's not to say that it's impossible, but I'm not sure that being on the losing ticket is necessarily the way to get yourself elected to the top spot 4 years later...Even assuming Romney could win, Vice Presidents only get to do as much as the President will let them (related to "b", above). Before signaling that there might even be an interest in being considered, I think the Pauls need to sit down and discuss how much of a risk they'd be willing to take that Romney would give Rand significant responsibility, and whether it's worth giving up a prominent place in the Senate.
Personally, if deals are going to be made, I'd hold out for naming Ron to the Cabinet--maybe Secretary of the Treasury...