Our influence with the Republican Party has been on the wain since about two years into the Bush administration.
However, we can have some influence on McCain. at least he thinks he needs us to get elected. [I'm not sure that's true!?] The point of voting for Mitt or Thompson in the primaries is to drive home to McCain he better cultivate some conservative principles if he wants our help.
Plenty of time to back him later if that is your decision.
I voted for Huckabee, warts and all, and became a delegate. I’m not a big Huck fan, but see him as the best hope not only to do the things you mentioned, but also as the best chance - a thin one, to be sure - to dereil John McCain. With Romney out, Huckabee is the guy. If Huckabee had gotten out, Romney would be that guy. They are about the same to me, w/Huckabee slightly better on social issues/trade and Romney slightly better on domestic economy.