Good question about suspension.
Everything is pretty much original, as in 30 years old. I did replace the starter relay when it welded itself due to me trying to start with low battery. Otherwise, not much has been changed. Everything works.
What's unchanged: electrics, wiring, rubber hoses, lines, fuel filter, and so on and now that I've replaced the ABS computer, the ABS works again, or at least I think it does (lights no longer blink at me all the time).
To your question: I like how the bike rides. Seems stiff enough to handle, not like riding a marshmallow. It feels decent in the curves but I don't have much to compare it to, suspension-wise. Previous bike was a Honda 450 that I crashed.
I'm filled with remorse at not attending to regular maintenance and fluid changes and so on as many others on this forum seem to do on a regular basis.
I had a front fork oil leak once, about 10-15 years ago, had the local shop (not BMW) replace the seals and put in some fork oil (I have no idea how much) and the fork stopped leaking. The rear spring / shock I've always left at the middle setting which seems good. I don't really have anything to compare it to, but I'm not bottoming out and the tires seem to maintain contact with the road as I'm riding. Mind you, I'm pretty gentle on the bike and only about 3,000 km or fewer a year (we have a short season here and I'm also into sailing, camping, bicycling, etc etc).