I'm doing lots of holiday candy and cookie baking and I've been dipping various goodies and I'm using a good quality chocolate. If I melt slow and don't add anything (flavor, butter, cream) how many times can a use the chocolate.
You can continue to remelt and temper chocolate several times. Reseed with fresh chocolate if possible. However this in not indefinite. For good coating and or tempering ideally I don't think you should do it more than 2-3 times. You can always reuse the chocolate to add to mousses, icings, baking etc. In that way you can continue to melt and reheat it several times. It will though break down eventually so don't try to stretch it too far!
I don't reuse my leftover chocolate, but just make some simple 'bark' with the leftovers; for dark chocolate, just throw in some nuts, maybe some liqueur (SP?!); hazelnut and frangelico are my faves; spread it out on a parchment lined pan, and chill, then break into pieces. With white chocolate, i use dried cherries and a cherry flavoring for chocolate and almonds sprinkled on top. I did this a couple of years ago, when I way overestimated the amount of white chocolate I needed, and it turned out to be the hit of the season! My best compliment was from the French chef I was doing banquet work with!