Of course it would help roca, but the real question, is whether or not the extra oomph is worth the extra cost. That is something ultimately you would have to decide.
If you do heavy iMovie, and I mean HEAVY, yeah there is no reason not to get a Mac Pro. You will save time. If you are doing this for money, heck yeah, it will allow you to do more jobs.
Just realize the added cost since you would need a display and you would most likely need a few HDs as well as a few GBs of RAM. After market of course to save some cash. And you would need a display of course. But you might have one you want to use.
The idea of "pro apps" and "consumer apps" is a ridiculous notion. Since the iMac and the Mac Pro can run both, the Mac Pro in some cases of course. But it is all about how much time you want to save and how much you want to spend or save. I think people assume that "i-apps" mean consumer and thus you need a consumer machine.
The Mac Pro offers more power and upgradeablity, the iMac, well you know.
Here are benchmarks to give you an idea of what to expect over an iMac. I will get some more benchmarks when I have time.
http://www.macintouch.com/reviews/macpro/benchmarks.html