I also have that scanner and with a little effort you can get good results. The key with the v500 is to get alternative software for the scanner or to master the pro-settings for the scanner. If you check the histogram before scanning, you will get better results. Although renting the more expensive scanner sounds fun.
Spend last night playing with my new Epson V500 and achieved much better results with next settings:
-2400 DPIs. A good size to print and a lot more sharpen than higher resolutions. Acording to some users, higher resolutions stretch scans lens to its limits providing bad results.
-Using silverfast software. More and better controls of scanning settings.(this one is a must).
-Multiexposure on (silverfast feature). Much better colors. More vivid.
-Postproduction. Just some levels and sharpen adjust to match original slide.
I'm not in my computer right now, but maybe tomorrow I'll post one image here te see my results.
As I mentioned in a few other threads here, flatbeds are junk for scanning film. Most can't focus (they're set to a pre-focused setting), and even if they do, they can't deal with film curvature. You need a dedicated film scanner. Granted most films scanners also have problems with film curvature, but they can at least focus, and it's a bit easier to take measures to minimize curvature.
Unfortunately there are no more high quality scanners to buy new (that I'm aware of, anyway), but even the Plusteks will still give you a better scan than you can get from a flatbed, and they're not that expensive.
Ideally you'd want a Nikon '9000 with a glass film carrier, but I suspect the price of used ones are going to go up now that Nikon has discontinued it. If you have the bucks for it, tho, go for it. Otherwise check out the Plusteks.
Not bad, but sometimes i don't know why my V750 giving me amazing results with B&W or colors and another time the results are not so good or what you call so-so.