I think you may have missed why things changed. I would submit that there is less concern about electing a Roman Catholic because there are more RC's that are conservative. The RCC has always been affiliated with the liberal view, but since Reagan a lot of RC's have broken with that view.
Santorum appears devout but that is a positive among most Christians.
Historically, Catholics were Democrats (though Senator Joe McCarthy was a notable exception); however, as the Democrat devotion to abortion became obvious in the 1970s many moved to the GOP.
You are correct that a lot of Catholics have moved back to the Democrats, but I think that is largely BECAUSE the GOP ignored the social issues that brought Catholic support in the first place.
Nevertheless, the fact remains that, over the past few decades at least, the candidate who wins the Catholic vote will almost certainly win the White House.