It's pretty complex in there. Mice are partly mechanical things though. A lot of stuff is hard to repair these days. Those surface mount components are tiny, but switches may be easier to replace. Getting into the device can be tricky. If find with some things like remote controls you have to push and squeeze a bit to find where they click together. It is satisfying when you fix things.
!PIZZA
I definitely agree, doing a laptop or PC is one thing, but these small and complex things are what get me truly excited. It is soo satisfying when it works out.
With PCs you can usually just swap parts out. I have one I need to look at that has no video output and it uses motherboard graphics.