My best guess for why Santorum ran in the first place is still to get his google search page results to be something a little less degrading. And my best guess for why he was able to stick around so long is that he wasn't as loose a cannon as any of the other "not-Mitt" contenders. At least in so far as when he said things that were patently crazy or absurd, they weren't crazy in ways that were likely to offend potential conservative voters in a GOP primary. So to summarize:
1) I think it was instructive to have Santorum giving voice to a series of conservative views, particularly as they relate to women and sexuality. These views exist, and they are part of the infrastructure behind anti-abortion politics, health care politics, sex education in schools, etc. I'm glad they finally got out in the open. I don't think they would have without Santorum being around in prominence. I'm not sure that these are necessarily well-thought out basis for most people, as is the case with most individual political views. But I do suspect that a certain level of discomfort with young women having relative control over their own sexual identity and lives therein is involved in the birth control debate and the others. I personally thought the smartest move was to make birth control OTC, which would make it cheaper and more accessible, and possibly to subsidize it for the poor, as we in effect already do with funding for planned parenthood. The opposition by conservatives on these two views was often just as extreme as the opposition to the ill-thought out health insurance mandate concerning birth control. Which to me suggests that the problem, for them, is women, particularly teens and coeds, using birth control and not government control. (Making birth control OTC would make it less regulated for instance, supposedly a good conservative goal).
2) I don't think it was instructive to see that there was a large contingent of GOP voters who are lukewarm at best concerning Mitt Romney. This was almost a given from observing his previous Presidential candidacy run in 2008, the relative indifference to Mormons among some base GOP voters (which is, admittedly and embarrassingly, less common than the level of animosity presented by liberals toward Mormons), and most pressing, his past positions on health care (and abortion) and overall rhetoric concerning the economy and wealth making him a less than ideal candidate for this race to many conservatives. This feature of the race was a foregone element, and it was amusing watching it glob onto a series of mediocre candidates (including Santorum, but mostly prominently Cain and Gingrich and Perry). And equally amusing to see that it largely, though not entirely, avoided Ron Paul. Mostly because of his foreign policy views being persona non grata for Republicans (though he had other interesting and enlightening moments, such as his invocation of the golden rule being booed by conservative audiences and his support of DADT repeal being at odds with the bulk of his party). I don't consider the Congressman someone I would support in an election per se, for a variety of policy and rhetorical differences (most especially on the Federal Reserve, where I also have reservations about Johnson and the "mainstream" Libertarian party as a whole for the amount of influence wielded by Austrian goldbug types). But he was at least less toxic than most of these idiots and it was very amusing watching conservatives, even self-described "tea-party" types, spewing bile and hatred at his very mention, followed only by some shudder of revulsion for Romney.
3) Elevating people like Santorum or Gingrich or Perry or Cain is instructive, in that it demonstrates a concern more for invective rather than conviction or principles, and in particular for invective opposing liberals rather than any importance on any "meaningful" policy grounds (such as, say, the deficit or economic growth). It also largely suggests that the most central economic ground for the GOP to fight over is tax policy. Which other than major reforms to simplify and restructure subsidies and tax credits (few of which enjoy conservative support), has few proposals likely to have any impact, positively or negatively, on growth and has several which do nothing about deficit closure to boot. So that's fun. And then it means that the culture war truce that a more sane conservative figure might advocate (Mitch Daniels or maybe Chris Christie) isn't going to happen.