I agree with your position. Obviously Gary isn't Dr. Paul, but I believe he's MUCH better than the alternatives on the ballot. Paul write-in votes won't be counted in my state, so I see a vote for Johnson as a way to voice dissatisfaction (and actually be counted). The 5% number would be great, primarily just to give a more viable avenue for liberty supporters.
As I understand his platform, he supports defending Israel but would not follow them into a war that they initiated. He is also in favor of removing foreign aid to all countries including Israel. Again, not the ideal non-interventionist policy of Dr. Paul, but certainly a better option than others on the ballot. I'm certainly no Johnson expert though, so I could be wrong.
When it comes down to it, we should all vote the way we want to vote. If you want to vote for Dr. Paul on principle, do it. If you want to vote for Gary Johnson for the 5% goal, do it. I am seeing a lot of my friends considering Gary Johnson though, which is highly unusual for my die hard Democrats/Republican friends. Perhaps a very small sign of more open-minded times?