I guess it depends on what you consider a “side set”. Like you, I have my nickel set and my type set as mains. Then is trails off into about 30 other very incomplete sets that will most likely never be completed. 2 coins here. Three coins there. Mercs, Walkers, Barber quarters, large cents. I have a little bit of a lot of stuff. Once I get away from the nickel collection, I mainly buy coins by eye appeal. Doesn't really matter what it is. Maybe one of these days I will try to concentrate my efforts to another series. Until then, I just collect coins.