Pretty nice! This is the game I would rather see running on Commodore Plus/4:
- faster bitmap rendering overall;
- you've already accepted some eventual colour clashes in order to use more colors for the 3D items, so a bitmap format with 2 fixed + 2 selectable colors wouldn't change that so much;
- one hw sprite only, easily portable to something XORred via software.
I would pay for a Plus/4 version of this. Keep up the great work!