My K1 rides smoother than the motoheap because I spent a couple of days getting it dialed in and tuned up. I also installed low mile coils and spark plug leads from a parts bike as well as replacing the rubber and plastic between the TBs and the head along with installing freshly reconditioned fuel injectors. Between that and the dealer replacing the steering head and final drive pivot bearings and drive shaft, it pretty much rides like a new bike.
Drawbacks:
It has the turning radius of a Mac truck. I suspect they did that to keep the mirrors from hitting the fairing. Don't expect to be pulling any single turn U-turns on 2-lane roads. I was able to scoot around in gas stations and such so it's not really that bad though. More of a minor annoyance really.
Lack of storage. It has three "glove compartments", one on each side of the rear and another in the right front of the fairing. You also have the standard K bike tank bag that you can use. I tried using it with the middle extension part installed to maximize storage but my helmet's chin bar would hit it when turning my head. Besides, it looks pretty stupid to boot so I don't consider using the center tank bag section to be a viable option. If you're going to hotel/motel it though some sort of dry bag on the rear would work for touring. The bike I got had 82k on it when I bought it and I doubt those were all "city" miles.
Ergos. You know, with the set back pegs I thought the ergos would be an issue. But I was able to do back to back 14 hour days w/o a problem. I was wearing Kevlar-lined jeans though. With a 34" inseam I think my knees would bang the fairing if I were wearing pants with CE armor. You could install "normal" peg plates for a more standard K bike riding position but you'd have to hack the fairing lowers up some for your toes and the brake/shift levers. For me I'm sure that modding the seat to move the rider back a bit would help.
Parts availability. For the suspension, wheels, engine and drive train you're good since all of the K bikes are so similar but when you get to body parts there aren't a load of good used ones floating around. I've heard estimates that only from 600-700 sold in the US. And there's a fair number of collector types who have one in their garage as dust collectors so they're not getting parted out frequently on Flebay and other places very often.
Seat. Sucks. What stock K bike seat doesn't though? I will sell the one I bought soon (mostly because I have several others and like to take a lot with me when touring since I like to camp) but if I were going to keep it I'd pay $319 to Rick Mayer and have him redo the seat to be more comfy and move the rider back a bit but for now an Alaska butt pad will suffice.
It's all K though and a hoot to ride. I once looked at them with disdain. Putting a few thousands miles on one let me understand the K1's virtues.
The K1100RS is the best classic K bike ever made. Ask Johnny.
K75Ss are good looking but they give no knee protection (I've frozen my kness on one riding in cold weather) and the way the instrument cluster bounces around is annoying.
I still am a big fan of K75s though. I ran some errands on mine yesterday and enjoy riding the snot out of it. My winter project is to give it a K1100RS fairing and mount the radials I've got for it.