A decade ago, after a few years of riding 1980 Honda CB750's, I knew I was ready for a better bike but something not too expensive. I had fallen in with BMW riders - some promoted airheads, some the early K-bikes. I learned that the airheads required more frequent service, the K's considerably less. As a non-mechanic, that would have sealed the deal even if I didn't like the K's better - and I did.
Correct me if I am wrong about any of the following:
Airheads do require fairly frequent service, but a decent "shade tree" mechanic can do almost everything. Parts are still available and fairly cheap. The real problem areas on some models have been resolved with more modern components. They last a long time in both years and miles if they are regularly (but cheaply) looked after.
The early K-bikes (before '91 or '92) would soon need front fork seals, a new rear shock, a new saddle, and most likely a replacement for the final drive spline. The latter was the"biggie," but still for well under $1000. Then you just ride her for 300-400K miles, doing the regular maintenance stuff and fixing the occasional problem. Maybe adjust the valves every 50K miles. That was the story on 1987 K75 until it died in a crash.
My current '92 K100RS and friend's GS1150 have one thing in common, non-functioning ABS. My friend took his bike to the local dealer and paid $300 to be told he needed a $2000 part. He tried to buy it used from someone in England and got ripped off. I'm still waiting for a local repair shop owned by a guy I trust to get the download for his latest gizmo so he can really read the problem. ABS is good on a car and should be even better on a bike the rare times you need it. (Cars skid, bikes fall over.) But spending $2000 on a bike probably worth no more than $4000 if perfect? I"ve had two Subaru cars with ABS, used it seriously twice, combined mileage about 500K, and no problems with either car. I ride without ABS protection.
The final drive issue with R bikes seems to be huge. Unless I'm wrong, nobody has come up with a permanent fix which they did with the early K bikes.
Which brings me to the real question about the "latest and greatest" accessories available on modern BMW's. I mean things like electric windshields, traction control, heated grips and seats, tire pressure monitors, etc. Do you think they will still be working for many years after your bike is out of waurantee? Or do you plan to buy insurance that will cover what all seem to be very expensive repairs or replacements?
Musing about it in this post, perhaps I'm better off to fix the ABS once I get it diagnosed, get a new rear shock for my low mileage bike, and otherwise just keeping the known problems which will surely crop up fixed. It might actually be both cheaper and problem free than buying a newish or even new bike.