I've only been here for 10 years, so I may not be an "experienced" user, but I have never once used the prefix selector. I didn't even see it until you mentioned it, and I went looking. I occasionally see a post with "S/V/C" in it, and I've come to recognize that as FWD stuff, which I tend to ignore as I don't know enough about them.
Other than that, unless EVERY post is required to have a prefix attached, I don't see the value in the feature at all. Example: If I want to see only 740 specific posts, there's a whopping 3 posts shown. Searching for "740" returns "Sorry - no matches" (minimum 4 characters required). Searching for "740*" returns pages and pages, but ONLY those that have "extended" terms in them... 740t, 740s, 740GL, etc. It also missed 1 of the 3 740-prefixed posts, because it didn't actually have an extended 740 "term" in it.
Putting what car it is in either the title, or the first few lines of the first post seems a lot more efficient than the "prefix" method. Just my 5 cents (we don't have pennies any more).