Actually, as I like to do thing so I can use them and doing things because they can be done doesn't appeal to me, there's no gameplay motivation to build anything but a manned craft, fuel station and tons of debris. Space station has some (a bit more with 0,23) use - I can refuel and now, when I've put science lab in my station experiments on my landing pod can be reset. No use for rovers (I've never really left Kerbin's SOI, but well, with them moving around the planets is just a bit faster and large distances are easier to cover with a rocket, at least without atmosphere). Totally no use for a base. Probes - well only point I see is to make one way trips, when you can't return.