Michael Brendan Dougherty's profile of Mark Sanford makes for interesting reading; so do the follow-ups from Reihan (here and here) and Larison. You can imagine a very ideologically interesting Republican primary in which a figure like Sanford came on strong as a more mainstream version of Ron Paul (small-government rigor plus foreign-policy noninterventionism, minus the nutty-uncle factor), while someone like, say, Jon Huntsman ended up representing the party's moderate wing. It could be a Goldwater-Rockefeller race for the new millenium - potentially disastrous for the party, sure, but potentially fruitful as well.
Then again, you could have imagined a very ideologically interesting Republican primary featuring a cast of characters as diverse as Rudy Giuliani, Mike Huckabee, Mitt Romney and John McCain - but instead, they mostly fell over one another trying to play a caricature of Ronald Reagan. The process of running for president isn't kind to ideological outliers (unless they're nothing-to-lose figures like Paul), which is why Mark Sanford, presidential candidate, might turn out to be a lot less interesting than the guy who shows up in Dougherty's profile.