Yeah... make sure you give it a good look over. There are exceptions, but you usually get what you pay for, and it could have been on the curb for good reason.

If it is good, ENOs are golden. I see nothing wrong with putting $$ into a good wheelset. You got the frame for free! My backup road bike is a $35 thrift store Sekai with $250 Mavic Ksyriums, and I love it. I don't think people realize what a difference wheels make. Occasionally I would have customers try the same road bike with Alex/Formula, then Mavic Ksyriums, then Rolfs, then Shimano 550s, and maybe some handbuilts if we had any around. In each case, it is like riding a completely different bike. If they are looking to spend the $$, then pull out carbon wheels and start having some real fun...