Are prices way down on classic muscle right now?

If you are doing one to make money with, treat it like a house. Make it nice, have great "Curb appeal,"/ broadest appeal, tasteful 'renovations,' make it user-friendly, and don't customize it to your taste.

Super custom motor/powertrain? Stupid.
$20K body & paint work? Stupid.
Ultra trick suspension/wheels/tires? Stupid.
"Glove" leather interior? Stupid.
Date-coded/NOS, concourse resto? Stupid- unless you really have something WAY out of the norm...and even then it's questionable

You can never make money with that kind of stuff in a 'normal' or slightly down economy. If you want or are planning to do any of that, well, keep the car and enjoy it.