Yes, I was thinking of adding "pixel breakpoints" (a specialized form of the regular memory watches, with some logic to convert pixel coordinates to VRAM). I didn't get around to actually doing it, but I did add a command to fill the VRAM with random data, so I could stop before a CALL, random the VRAM, execute the CALL, and see what that particular routine was doing.

NES - no idea, I've only done ZX Spectrum and PC. But you should still be able to read the emulated RAM and make a new renderer from that data.