I've thought about getting rims, but the optimum rim in my opinion would probably be an 18", which seems to be the most expensive choice out there. Tires for 20s seem to be cheaper than either 17s or 18s, and 20s just look too big to me. So I'm sticking with the factory 16s for now.
We recently had someone claim to bust a tire on one of our jobsites. I checked the prices for his size tire, and they turned out to be $175 for those crappy factory General tires in a 255-70R17 size!