Thanks for the opinions. I'll mull it over for a bit. I kind of like the idea of seeing if I can get it working for not too much $$. If so, makes sense to either sell it as working/original, or do a full-on restore. But I don't really want to spend hundreds to get it working, and I don't have quite enough electronics expertise to truly troubleshoot it down to the diode. For now it will occupy a space in the garage while I finish my first MAME cab.
BTW the game itself is like Space Invaders, with the rows of aliens descending toward earth, but you twist the two joysticks to aim a barrel and fire away at them with silver balls. At the top and sides are a series of targets. I think it basically does some math to figure out which alien you would have to roll over first in order to hit that target. It was apparently a straight-up copy of William's Hyper Ball.