I wouldn't give up in the 3V boards, they're very repairable. For the ones with only the sound out, I know that both GGG and I have brought a number of those back. Other stuff like speed control issues are usually pretty easy to fix as well.
For the 5V boards, I limit myself to FET replacements for various I/O functions, the audio amplifier, and the one large capacitor that seems to be the most common cap failure. All of these are done without separating the boards.