Can’t help you with the beer itself, but we opened a 1984 bottle of Bruocsella Grand Cru two years ago and it was very tasty. So yeah, it could be good.
There are some facebook groups where you might have more luck then here … If you need pointers write me a pm … I think 1982 should be doable. Value depends on the bottle (and probably also brewery)
If the bottle was stored properly there is a good chance you will get something nice. I would say a higher chance with a Geuze then fruited beers. If I was to aquire a bottle I would ask about storing conditions (and number of previous owners), but especially fill levels. If fill levels are low there is a high chance you get an (expensive) bottle of vinegar…
The easiest is trading for something that’s equal old, then the value is on a similar base. Otherwise of course hard to tell, it’s mostly a “what are you willing to trade” and “am I comfortable with giving it away”…for some old beers one can take alook at beerblackbook but you need to abstract the crazy factor to get to a realistic price. Crazy factor again raises when a beer gets older so I think I’m turing around in a circle.
Often people have already a vision of what they want in exchange for older stuff.