Cool for you! The JC-120 is a great amp. In fact, I don't know off-hand of any other solid-state amp I would ever recommend. General value of a used one around here is in the ballpark of $400, +/- $50 depending on cosmetics, etc.
When I play festival gigs where the sound company provides a backline, I'm always relieved when a JC-120 is available. They always sound good, they react well to pedals, and they are amazingly loud and clean and clear-sounding.
Older ones are not 'vintage' (e.g. 'valuable'

, at least not yet- not in the same way vintage tube amps can appreciate. It could happen that some famous guy will use one prominently, and then the value could skyrocket. It has happened with other stuff.
But for now; you got a great amp, enjoy it.
-dave