It would be like going back and saying I want to learn how to use a slide ruler again? Sure you can do it, but why? I am telling you that all the components on that board are beyond useful life. Are you going to change every capacitor, diode, FET? It is also multilayer board so do not be surprised if you tear traces you do not have access too.
Stick to the simple stuff. Motor function, Sound, lights? If it starts doing weird stuff, your most likely at the processor which you can't fix or program if you had one.
I have a board right now that starts up after a 15sec delay, but only headlight comes on. No other function. How are you going to fix that?
Everyone has moved on to better functions like quillable whistle, bigger sound files, whistle smoke, rule 17.
If you wanted to concentrate on something, look at the 3V board and start looking at PS-3. Get ahead of the curve:-) G