If you can actually find good wheels that are the size you need from a "free" bike you could make a lot of improvement over steel rims. It is amazing how many people have great bike part stuff hanging around their garage left over from a upgrade. Try posting an ad on the forum or Craigslist for your desired parts and people will often go out of their way to help.

Unless you have a reason to need super strong rims (jumping curbs, drain guard flipping, etc) the more you do to improve your wheels the more you will love your ride.