Update: 138,000 miles
The bike has slightly over 138,000 miles on the odometer now, and today I changed the 10-40 oil and the Kawasaki oil filter. First filter change since 95,680 miles, and I was a bit curious to see if there would be any metal dust or debris present. A 2X lens and a good light showed NONE. No metal, no sludge. I change the oil twice a year and almost always ride the bike for a 45-65 mile run on the highway, avoiding weather too hot (over 90F), too cold (under 65) or rainy.
I ride rather gently most of the time, and I don't run it up to 8000 rpm in the gears all the time. If I really want to accelerate I run it up to 9 or 10 because the best torque comes in from 9 to 11. But I never run it over 11, and rarely over 10. Most of my riding is on the highway at a steady 65 mph. I end up with about 75 mpg with the routine I have. I use the machine purely for sport and just have a regular route where I enjoy the machine and the environment, with minimum risk.
The complete electrical system on this bike has never been touched, except for bulbs, batteries and a couple of turn signal relays.
The steering head and rear fork bearings have never yet needed any attention. All the original cables are still in place and functional, including the speedo cable, which I think I lubed with moly grease about ten years ago. The speedo needle is not jiggling yet, so the lubrication must still be satisfactory. All the gauges work like new. The front and rear brake pads have been replaced once.
OEM tires last 22,000 miles front and 11,000 rear. The chain and sprockets last 22,000, and I change them with the front tire. I apply 90 wt gear oil to the chain every 500 miles. This keeps it in good condition. I use the 14 and 42 sprocket combination, which gives the best gear ratio for all around use: 8000 rpm at 70 mph. The bike cruises fine at 70-75 mph, giving 75 mpg on the spec 87 fuel.
The engine starts instantly from cold by full application of the choke lever with the hand off the twistgrip. The engine idles at 1100 rpm cold with the 10-40 oil, then idles at 1300 rpm when the oil warms up.
The carburetors on this bike have never been touched from new (this is the second engine) and don't need it. They work perfectly. My philosophy is don't mess with parts that are working well.
So friends, what I am describing above is a motorcycling experience unbelievably good from every point of view, vastly better than the constant maintenance and repair we had to put up with 50+ years ago when I started riding.
My hat is off to the hard-working Kawasaki engineers, who have given such a high-quality product to the public, especially for such a low price. Craigslist where I live always has a selection of perfect, low-mileage 250 Ninjas available for a big discount off the new prices, and that's the way to go, as long as you get the 'right' bike that is sound and hasn't been abused.