I could understand either the plural or singular version of this domain making sense but, I would estimate for an end-user they are more likely to want the singular (recognizing the plural is an option). Have you thought about an end-user or who you might target for resale?
It is a very relevant name to a generation of youth who live for "tonight" and like to go out "tonight." Listen to contemporary pop music. If you could tag or find one word common in almost all of these club, dance, and party songs, it would be "tonight." That's when everything happens, that's when they want it to happen, etc. I have actually thought about this awhile. This would be a great domain to build off of that excitement and interest. Perhaps you are looking at end-users in music, fashion, pop culture, etc.
If it were me, I would lowball at $100 like Menzl said. Perhaps wait till it's closer to expiration. If you're not committed to marketing and getting rid of it or developing it, that $35 a year really could pile up.