An interesting theory, but my gut (and some of that polling data) tells me they might be better off going with Bostic, precisely because he doesn’t have Sanford’s baggage. I’m not stupid enough to urge a vote against Sanford if he is the nominee, but I believe he is more of a lightning rod for the opposition. Ultimately, I believe this is more personal for Sanford, looking for redemption. That can be a risky and questionable motive for public office, because you’re making it about yourself and not your constituents. Sometimes I can agree with it, and sometimes I can’t. In this instance, I lean against.
I would take a PPP poll on that race with a heaping tablespoon of salt. Besides, IIRC, PPP had Bostic up by 1 and Sanford down 2 or something like that, so not even PPP has Bostic doing much better than Sanford in the general.
Here’s a recent NRO post on the race: http://www.nationalreview.com/corner/344299/mark-sanford-taxpayers-choice-congress-deroy-murdock