I have 3 microscopes that I like for different purposes (well, one I like for the purpose of "just in case the other two break," I hate that one). And I just scored a used dissecting microscope off ebay because my vet said I had to (it's for looking at horse embryos, should I be lucky enough to flush one).
I never get bored of looking at fish poop, tank water, scale scrapings, etc. A lot of the time I have no idea what I'm looking at, but I can't learn if I don't practice!