Motorcycles with low miles die from neglect, not use. Since most motorcycles fall into this category, the myth has perpetuated that they're "used up" by 20-30k. You'd experience the same thing with a 10-year-old car that only had 30k on it.
Riding 60 miles a day, with proper maintenance, is the best thing you can do to your bike. I expect 100k at the very low end out of it. Probably a lot more.
Ding ding ding ding.
Low mileage used bikes scare me. Likely owned by someone in a mid life crisis who may have never changed the oil, certainly never took the time to change fluids and the like (brake fluid, coolant, etc.), and likely let it sit for months at a time; then fired it up and took for for a short ride and came back.
I'm at 30k on mine and she is running like when brand new. Starts up instantly, runs wherever I need to go, motor is strong. I absolutely expect 100k out of her and only that much because about the time I hit 100k, is about the time I'm planning on maybe moving up to a full size touring bike.
There is more than one 100k+ VN900 out there. Big Toe had over 150k on his and had NEVER DONE THE VALVE ADJUSTMENTS! He had to replace his valves do to them finally burning some 130k overdue for maintenance, but that thing took a beating! He used conventional oil and followed Kawasaki's service schedule.
Treat it right, keep it maintained, she'll run forever.
I put a lot of miles on my vehicles each year (around 60k). I have had more than one 500,000 mile car, with no major repairs, and typical maintenance. I firmly believe that vehicles that are used regularly and have a decent amount of miles put on them last longer. You ride/drive it enough to notice issues early, you maintain it at good intervals because of the mileage (so fluids don't sit and break down), and the engine spends more time warmed up and operating, as opposed to short stop-and-go runs, which are hard on the motor. A great example there is city fire trucks vs. the road tractors they are based on. My sister is a firefighter in a big city. They have all sorts of mechanical issues, all the time. They are a freightliner chassis with a detroit diesel. It's not uncommon for them to need a complete teardown and rebuild of those engines at 50k. Yet, it's not uncommon for a freightliner road tractor with the same engine to get a million miles between rebuilds. The reason? The fire department only goes 4 or 5 miles most of the time on a call. The engines rarely get warmed up completely, and every second counts so the engines never get any idle time before taking off, just crank and go. That's a LOT harder on a motor, than 10x as many miles on the highway, or properly warmed up first (not up to operating temp, but a good minute of idle time before taking off), or ridden/driven every day long enough to get the engine completely warmed up.
Not an engineer, not a mechanic. But, that's what I've observed. Just seems like vehicles that get driven last, and vehicles that sit don't.
There are also certain un-named brands of air-cooled motorcycles and certain engines in their line known to be rebuilt every 30-50k or so. A friend of mine has a 2005 Har.. er.. un-named brand with 26k on it that he just had rebuilt. Another friend has the same bike, 110k miles, rebuilt twice. So, not every bike is equal. Heck, even Kawasaki has had some real duds. But the Vulcan 900 motor is a strong motor that has a proven track record of long reliability.
