Are you running carbon rims?
I assume not. If so, get training wheels to save the carbon wheels.
If you aren't, you're really not wearing the rim at all by braking. Really, it'll be fine.
Most likely you just have crappy brake pads. I suggest getting some Swisstop Green pads. I just started using those, they brake scary fast. I haven't used them extensively in the wet, but they're supposed to work almost better than in the dry.
A much simpler, cheaper solution that changing bikes // getting a disc brake setup.
For the long descents, I would use the rear disk brake more than the front rim, thus sparing the rim. Also, in wet conditions at least one of my brakes would be relatively unaffected. A friend has tried to steer me away from disc brakes on a road bike, claiming that the likelihood of locking the wheel and possibly taking a spill wouldn’t be worth the upside.
EDIT: Yeah, he's exactly right. I forgot to mention that part. When I read you saying you wanted a disc on the rear, I was going to say what a bad plan that was, then saw what your friend said. Go try this in the dry: Get up to a medium speed, try to brake as fast as you comfortably can using only the front brake. Now, do the same with the rear. Notice how the rear locks up really easily? If ANYTHING, you'd want the disc on the front. That said, you don't need disc brakes on a road bike.
If you're buying a brand new commuter only hybrid, for instance, and there's a disc brake model? I guess you could get it. Would I feel 100% comfortable using good dual pivot (road bike) brakes with good pads in the rain? Yep, do it all the time.