Obviously, check out what the piece would be worth as it is. Let's say your pistol is pretty common, has no provinence (ie it wasn't owned by somebody famous) and is in pretty rough shape. It's value as a collector piece is going to be pretty low. If you own it as a shooter, then reblueing will not make that much difference. On the other hand, if it's a valuable item, a collector prize, then refinishing is not a good idea at all.