There were many miles on this bike when I got it, but it had been well maintained by the previous owners, so there wasn't a particular downside to that. I already knew the mileage wasn't a real factor, it was how often the oil had been changed that counted. I knew the previous owners didn't thrash the bike very much.
In the 100,000 miles or so I put on it, the original cycle parts; frame, driveline, forks, electrics, etc, just carried on doing what they do. Only now are the front forks at the end of life, and they can be re-bushed and re-chromed if I want to do that.
I have a stock of spares built up, so will swap out the forks.
The usual Achilles heel on these is the reg-rec, and from what I found on the GSResources site, it's caused by the form of shunt regulation that causes excess current to be dumped back through the stator windings, thus ensuring the stator is under maximum load, especially when you run with no lights on. Paradoxically, you have to have the headlamp on to give the stator an easier time, by using some of its output and not letting the reg-rec dump it all back into the windings. A thirty year old stator doesn't take kindly to this.
There is now a newer design of reg-rec from Shindengen, known as the SH-775, made for Polaris ATVs, which gets around this problem and makes the stator run cooler. I've fitted one of these so will see how it pans out.
Owner stupidity can kill the engine - I was in the habit of letting it warm up for five minutes on the centre stand every morning, but one day I went to leave too quickly, jammed it into gear and twisted a crank journal (pressed-together crank) because of cold oil clutch drag.
That engine awaits stripdown, and the bike now has an American import engine that came over in a container full of Mid-West cruisers. The replacement engine now has over 30K on it, and many years of life in it yet.