Doing "sort-of-OK in 2012" against Barack Obama (who, I believe, will have a successful first term as President because he has the skills needed to be at the least an average-achiever as Presidents go) will put him in a good position in which to win in 2016 against a clueless or terribly-flawed would-be Democratic successor to Obama or in the aftermath of a knock-down, drag-out primary season by Democrats in 2016. So long as people get the impression that Crist would win "except that he is facing Barack Obama", he would be well-positioned for 2016. Think of Thomas E. Dewey in 1944; he lost handily to FDR and nearly beat Harry Truman in 1948.
This is "sort of OK" for Crist in 2012:
and this is what I see for Huckabee:
and Romney:
Second terms of most Presidents are weaker than the first, and by the end of most second terms, the opposition party has considerable advantages. By 2016 the Republican Party leadership will have come to recognize (one hopes!) that the base that it relied upon between 1980 and 2008 can't win on its own, and that to win
the nationwide election it will be obliged to make compromises that assuage the concerns of people who have found the Gingrich-Dubya GOP culture alien. It may come up with fresh ideas with which to reform what Obama botched or missed. It might also challenge some weak or corrupt Democratic politicians, as any party that gets into power brings some not-so-desirable characters with it.
If both Obama and Crist look good in 2012, then Obama wins. Incumbency has its advantages if one is competent and relevant. No landslide this time, but Obama can lose a little from 2008 and still win. But if the GOP nominates some character from the Hard Right in 2008 to face Obama, then Obama wins in a landslide. That might still leave a good opening for Crist in 2016.
Republicans, I think that Crist is your man to challenge Obama in 2012 and look good losing, only to have a good chance of winning in 2016.