I think the lukewarm support of the evangelical community will actually help Rudy in the general election. The key to the 2008 election is the moderate independents. These people tend to be conservative on economic and security issues but liberal or libertarian in social issues. They tend to be very suspicious of any candidate too enthusiastically supported by the Evangelical Christians. I think for every hardline conservative vote that Rudy loses, he picks up 2 from the moderate independents.
I have a "George Allen" concern about Fred Thompson. Prior to the elections of 2006, I was an enthusiastic Allen supporter thinking this is our guy for 2008. I have this nagging doubt that Thompsom might not be ready for primetime just like Allen wasn't.
I weekly attend a conservative, reformed, evangelical church. Our pastor and his family definitely would NOT support Rudy but most of the congregation would even though Rudy is not anyone's first choice.
One of the main reasons Brownback and Hunter are where they are at 1% is their inability to attract a and b.
That's precisely the calculus that has Rudy where he is in the polls. Evangelicals and hardline conservatives (FR included) are influential, but often mistake influence for raw numbers. Simply put, we don't have the raw numbers that we often think we do, especially in comparison to the "fiscally conservative/socially liberal" independents. These moderates float back and forth, but can easily be scared away by extremists of either side.
The harder that evangelicals scream at Rudy, the more moderates will get on board with him. It de-stigmatizes voting Republican, if you will, among certain segments of society. It may sacrifice 15% of the hard right, but it will, as you noted, gain 30% of the center in exchange.