There might be a date inside the cabinet; there often is. Other than that, no way I know of to date it more accurately than by the years it was in the catalogs.
If you want to sell them, someone will buy them. Sound is, as always, a personal decision.
I have no idea what would work best for you. I'm a bass player, anyway.
The actual monetary value of anything is determined by agreement between the buyer and seller. Anything else is just a guess. You could try looking on ebay to see if such a transaction has taken place recently, and what the price paid was.
Originally, the wheels were on the side of the cabinet, the rubber feet on the bottom. That way, you could wheel it into position, then tip it onto its feet for use. Looked a little goofy, with the wheels sticking out the side, but it was really very practical.
