I'm a wheel whore. I can't have enough wheels. Six wheelsets, plus a trainer-specific wheel is not too many wheels for two bikes... It's all about having the right tool for the job.
Through some wheeling and dealing, I just picked up a set of Campy Record/Mavic Reflex tubulars 32h laced 3x. The main reason I got them is for ultra nasty CX race conditions (more to not destroy my carbon hoops than to have a more conditions-appropriate wheelset). Side benefit to the wheels was that they came into my possession with road tubies already glued to them. Sweet. Rather than just rip off the tires, I decided to get at least one ride on them.
Holy smokes...those babies roll ultra smooth. I was amazed at how instantly I noticed the difference between theses and my regular training wheels (32h Veloce hubs/Mavic Open Sport hoops). I'm sure the biggest reason for that is the tubulars, followed closely by the box section rim without stiffening benefits of the clincher hooks. Having Campy's tried-and-true cup & cone bearings does not hurt, either. It also doesn't hurt that I rebuilt these wheels back in December 07, while playing mechanic to the stars when they were still in the possession of Superstar RDK.
Add in the 2.5 wheelsets for my MTB and you can understand why I'm a wheel whore.
Hell, I even have 2 sets of wheels for my car; one for summer, one for winter.