My $0.02... unless you've got money to burn... this is a waste of money. I recently picked up some 45mm carbon rims and I can't really tell a difference in speed between them and my old aluminum rims... maybe a tiny bit but i think that would be mostly a placebo effect and that's riding solo. If you're riding in a group the aero benefits of carbon wheels will be even lower since you're already getting the aero advantage of being in the draft.
They look cool and sound cool but if you're getting them to try and make a noticeable difference in keeping up on group rides... I doubt it's going to help.
That said... swapping brake pads is just a couple minute job so as long as the rim widths are similar between the wheels you buy swapping wheels isn't that big of a deal unless you were going to be doing it daily. Performance bike has had some good deals on the older style reynolds carbon clinchers (under $1000 today)