Well there's what the manual says and what people do and everyone is different in their use/abuse and maintinence/ or lack of.
Personally based off how I ride a bike which is 95% offroad and would be concidered a clutch abuser and enjoy the higher end of the rpm spectrum....
-I change oil every 2-300 miles depending on my guilt from abuse... If I did a race or road it like it was a race it may be much sooner and only be 60-100 miles.
- I change/clean the airfilter when it no longer looks clean (every 2-3 rides?)
- I like to know what the valves are doing- so I'd check when new, then at least once a season or maybe twice a season depending on their stability.
- engine rebuilds- they have been stable but this really varies with use and abuse and the maintinence you asked about. I will probably rebuild when my valves start to become unstable (need adjustments quicker and quicker- leeding to the inevidable rebuild) mine have lossend only .001" in around 10,000 miles so Things are looking pretty darn good with 1 adjustment in 4 seasons!
but that's me... hope it gives you some insight