You have a really excellent camera that should still have plenty of life left in it. It will give you access to the famed Zeiss T* lenses that range from fish-eye to super telephoto, though some prices are eye-watering for the more exotic optics. If on a budget, then the Yashica lens range also uses the C/Y bayonet (Contax/Yashica), and there are lenses from third-party suppliers; some cheap and nasty, some expensive and desirable.
You can attach a range of different flash units, change the focusing screens, add a motor-drive, or replace the back with a data back.
It's a system camera, and you can tailor it to your needs to quite an extent.
As for value, well it's worth as much as someone is prepared to pay for it! There will be enough on the market to make it almost disposable if it starts playing up - twenty- to thirty-year-old electronics.
Nick