In answer to your first question: I think $500 is a great price. Prices have been recently depressed, but this is still a good deal. I am biased in that I do not worry that much about a few scratches (not sure what to think about the holes on top however).
In answer to your second question: Refinishing them would be more work than you realize, especially if you have not done that sort of thing before. The job would be very time consuming since things need to have multiple steps of applications/sandings/ drying times etc. It is easy to underestimate the time involved to do a decent job and to do a great job is even worse.
You are probably right about the hiss being a function of the source and not the speaker. However, that does raise an interesting point about high efffeciency speakers. They are very revealing of any other flaws in the system.
Have you listened to them? Did you like them and was there sufficient deep bass? Unless the cabinets are very rough, I doubt they will last very long at that price.