Higher mileage doesn't mean its worthless but as miles tot up parts will start to wear out and running the bike will inevitably become more expensive as mileage increases.
My 748 has done nearly 23,000 miles now and runs as well as ever. Does use a bit of oil though.
I think that's an Italian trait Duke. The RSV uses a bit of oil, but nothing compared to my Alfa. I recon that used nearly as much oil as petrol.
Interesting about the comments on how an engine is used and lifetime. The track bike has never been road legal, and if it was a hire bike in a former life then it's spent must of it's life in 20 minute sprints bouncing of the limiter.
I'm no professional, but there are no obvious rattles or smoke when it's running. It does look to have been well looked after though. Maybe maintenance is more important, or maybe it's more to do with the engine being used for what it was designed for.
You never really learn to swear until you learn to drive.
If everything seems under control, you're not going fast enough - Mario Andretti
Definitely how it's used is a huge factor on engine wear but also maintenance and how it's looked after too is a significant factor.
I agree with all the above comments fully but my personal opinion is 20000 miles is high mileage for a bike. Not because it can't run reliably for 10 times that distance but because maintaining it and replacing chains, brakes, bearings, cooĺant hoses and other perishables, suspension, spark plugs, valve clearances (which a lot of owners miss) general mainteance plus the significantly higher depreciation after 20k make keeping it much more expensive than trading in imo
It also doesn't help that there are 4 year old bikes with between 2000 and 5000 on the clock so personally unless it's a keeper like Dukes 748 I would always offload a bike before 20k and never consider buying one unless they were absolutely giving it away. IMO it's just not worth the effort and if maintained properly is actually more expensive than trading in for something that will always be better.