Sorry, but you've got it backwards. It's Cain, Bachmann, and to a lesser extent Palin that have thin resumes of actual accomplishment.
Cain and Bachmann are no more qualified than the wave of Hope and Change that was Senator Barack Obama. You can project all kinds of wonderful acts on them, but the reality is, they've never been in the big chair. Just as the left had high hopes and dreams for Obama, for no reason other than his core beliefs, there's no reason to believe that Cain or Bachmann can live up to their talk once they're actually playing at the top tier. There just isn't. Being President is a lot more complex than campaigning, as Dear Leader the Barackulous Miracle is learning.
Palin had a truly stellar rising career that was cut short. At least with her, there are indications that she had the right stuff to be a big league contender. That said, being a half term governor of a low population, non-border state isn't the same animal as running 25 million constituents well for 10+ years. People are going to view it differently. Sure, Perry isn't pure, but he's been tested more thoroughly for what the job of the U.S. President actually is than the rest of the field combined. His overall record is very good, even if he has some awful black marks.
We can assume that other candidates would be better because they've never been tested, but it's just an assumption.
I guess 20 years in politics is cut short, Really? try harder next time