Enter the greatest thing ever SKS clip ons.
The rear is an X3 and since all my bikes are steel and have 27.2 posts I can move it from bike to bike without any adjustment. It takes literally 5 seconds to mount it and it's a life saver. It's true that it doesn't provide as much coverage as a full mount fender but it's light years better than nothing at all and unlike the kind of fender that clips onto your stays this one accomodates any tire size and never rubs on your tire.
The front is an X-Board and mounts with two plastic bands. I've had this one for the last 5 years and I think I paid like $12 for it. Not as much coverage as a full fender of course, but again it has none of the drawbacks. While I can and will sometimes mount a full rear fender to some of my bikes, I find front fenders in winter absolutely awful. When the going is really nasty and your front end is squirming around there's nothing more disheartening than clipping your foot on the front fender.
Clip ons, some of the benefits, none of the drawbacks and one set covers all of your bikes.
