Based on the responses, it sounds like I would probably benefit reasonably well from having improved trip. Tihocan kind of made a point that I didn't really think of - that I trip towards the end of the attack sequence. Since that gives me a higher attack bonus and also means I don't lose out on three other attacks, it should make tripping much easier to integrate into combat.
I'm also getting the impression that I shouldn't expect to keep the enemy down every time with my DC, which is what I really expected. Honestly if I could trip an enemy for a significant length (ie more than 5 second) at least about 1/3 to 1/2 of the time then it will be well worth it for me. I'm not expecting to able to be incredibly good at it, I just want it to be significantly worthwhile. It sounds like I should be albe to expect that.
Anyway, thanks for the advice everyone, and I appreciate you all taking the time to respond. I was just a little wary of making a bad feat choice this late in the build, as high-level dragonshards don't exactly grow on trees.