I see the logic, but I think there's a decent chance that because it's a caucus and not a primary, that whoever has the best organization (Perry) will be able to whip the caucuses into shape by day's end. Bachmann's support will be as fleeting in that state as John Edwards's was in 2008. Cain....well I don't take him seriously. He's ran to become a celebrity, sell some books and likely get a talk show on Fox News or elsewhere. The fact he became a frontrunner is a shock to him as much as us and he is clearly unprepared for it and isn't even seriously campaigning.
Taking Cain and Bachmann seriously is indeed ridiculous, but they will still have a decent amount of support in Iowa that would otherwise go to Perry. Same with Gingrich and Paul to a certain extent. And don't forget about Rick Santorum. Their support will be small and minimal, but it will take away from Perry quite a bit because there are just so many.
Don't forget that Romney still has a good amount of organization in Iowa. Last time around Romney got 25% of the vote in Iowa. And you also have to take into account that social conservatives had Mike Huckabee to coalesce around, they don't have that this time thanks to the social conservative faction being split between Perry, Cain, Bachmann, Santorum, and Gingrich. Some social conservatives are also starting to give Romney a second look because even they will admit that the economy is issue #1 in their eyes.
I didn't watch the debate. But I expect him to win because Nevada is not a Christian values conservative state and is honestly quite purple. Romney works in that environment and will run strong on the economy which is where Nevada hurts the most. Though comments like just "let the housing crisis bottom out by doing nothing" are sure to hurt him some in a general there.
The crowds cheered for Romney and booed Perry as he attacked him. As for the general election, I think Romney is the favorite in the state. Nevada is one of the worst hit states in the recession and going by the recent special election, it seems like the Democrats have given up on Washoe County, and you can't win Nevada without Washoe.
I don't think he'll win Iowa, so he'll have New Hampshire. Whoever wins in Iowa, likely Perry, will have some momentum going into South Carolina which is a very traditional, Christian, conservative state where social issues matter (this is the birthplace of the Civil War, after all). Romney isn't conservative enough for them on social issues, is a Mormon which may play a role in this particular primary (more than in any of the other early primaries) and will be viewed as a Northeasterner while Perry is a Southerner with a consistent ideological view.
Remember that John McCain won South Carolina in 2008 against the very traditional, Christian, social conservative, Southern governor Mike Huckabee. Most McCain voters will most likely end up going towards Mitt Romney which constitutes 33% of the vote. He'll have a lot of momentum for him if he wins Iowa. Endorsements from Jim DeMint (who endorsed Romney in 2008 and still has a very good relationship with Romney) and Nikki Haley (who is most likely to endorse Romney) would help him tremendously as well.
Even if Perry wins Iowa and South Carolina, Romney will win the other three and kill Perry come Super Tuesday. I'm just saying, I don't think it will be the clean sweep that you imagine. And if Perry can win Iowa and SC, he can become the one disgruntled Tea Partiers latch onto. A long shot though, to be sure.
Actually, Super Tuesday favors Rick Perry quite heavily. Alaska, Georgia, Idaho, Oklahoma, Tennessee, and Texas are states that would typically go for Perry. The only guaranteed states for Romney on Super Tuesday are Massachusetts and Vermont. And maybe Virginia and North Dakota will go for Romney, but those are big maybes.