It may be worth a lot - 20 years from now. I don't care what these guys said about NES cartridges - there are some cartridge games which sell for thousands of DOLLARS because they're considered classic. I remember hearing about one such game on screw-attack.
I have a sealed (original packaging) copy of PACMAN for the atari 5200...
I've tried to value it, but all the copies on E-Bay are opened.