NES games tend to have tiles in ROM, so for better or for worse, combining tiles isn't a speed issue, because it's not an option. The character bank in this release honestly has abundant free space. I just haven't committed to diagonals, or marching squares, or approximate 2x2 mini-tiles or whatever. Consoles like this deserve one and handhelds would absolutely require one.
Incidentally the Sega Master System would be fantastic for this. Flippable 16-color tiles, horizontal blanking interrupts, much more RAM. Expect cleaner and faster C code when the judging is over.