Via Wine Dark Sea, I found "Thomism and the Archaeology of Ideas" on a lovely website, The Canterbury Tales (Wow, that was a lot of links...).
Taylor basically summarizes the distinction between doing theology (or philosophy) in order to arrive at truth and simply doing a historical survey of when and where ideas appeared. This distinction is fascinating and is, in large part, why I left the Academy: so many careers and conversations are wholly devoted to the historical particulars that few people get around to asking, "But is it true?" Or they think that question is wholly facetious, a non-question. I wanted to do philosophy so that I could learn to die (ergo, learn to live) well.
That being said, I don't think the distinction finds a simple expression in real academicians. A teacher who longs to know "Is it true?" will also concern herself with the historical situation in which an idea arose--we are historical creatures, after all. And even the history buffs in the philosophy department sometimes make judgments about an idea's truth (in my grad program, most of them had no problem concluding that Thomism was untrue).
The Judeo-Christian tradition gave us the idea of progress in history, and that includes the history of ideas (although many philosophers then had a heyday with progress and made it into a god). So, once again, I'm falling on the "both-and" side of the debate. Because we are finite creatures, our forays into history--a biography of Thomas--can become, from our point of view, an infinitely inexhaustible project. A whole lifetime can be spent on tiny minutiae and historical trivia. We have to know when to stop and ask the bigger questions sometimes. Both-and.
We need historical research and the question "Is it true?" The important point is that our thirst for truth should guide our history; we should do history in order to learn truth. What we must not do is make history and contingency our only truth: all is changing, all is contingent, we can never know, on and on and on...