I'm hoping to build a swing set or something for my kids. The only formal thing we pay for is recreational youth soccer, so it's nice for the kids to have a platform for outside play while at home (which is most of the time, aside from school). I'm thinking I might end up making some sort of abstract structure instead, though, since the swing would just be a swing, whereas a tower would be a pirate ship, space ship, house, whatever.
I don't see the swing set as the problem. I see the combination of expensive purchase and lack of use as the problem, which the OP mentioned. It's the same problem as that of buying kids toys on a regular basis, just on a bigger scale.