I've got a 1987 R80RT with about 42,000 miles on it. The Achilles heel of the bike is the weak charging system; I aggravated the situation by having the dealer add MotoLights and heated grips when I bought it used three years ago. As a result I stranded myself a time or two, and since I was using it as a commuter ride I ended up buying a 1999 R1100RA a year later to get an acceptable level of reliability.
What I did not know at the time was that there is an electrical system upgrade that solves the problem (but is pricey at around $1000 with dealer installation). Had I known about it, I probably would have done it then rather than buy a second bike. Anyway, I finally did the upgrade last summer and now the bike is happy. I've accepted the fact that I'm never going to get the money out of the bike should I ever sell it.
The brakes on the 1987 R80RT are definitely a generation behind those on the 1999 R1100RA. I have a lot more confidence in braking on the newer bike. I recently added braided stainless steel brake lines to the front brake on the airhead, which improved braking response somewhat but not to the level of the oilhead.
I replaced the stock windshield with an aftermarket windshield from Parabellum. Much quieter, and well worth the money.
The airhead is an entirely different feel than the oilhead. Without a Telelever you can feel the fork dive on hard braking. But feels noticeably lighter than the oilhead, even though the actual difference is probably only about 50-60 lbs. Possibly this is due to a higher CG.
Weather protection is great. It's a wonderful ride in the winter as long as the roads are clear of ice.
Since I've had mine (purchased with about 33,000 miles), I've had the steering head bearings replaced, the electrical system upgraded, brake lines upgraded, master cylinder replaced, carburetors rebuilt, and a new left side head gasket, in addition to regular service. So hopefully the rehab is behind us and it's all regular maintenance from here on in. Parts availability is good.