I have a question that i always wondered about, why is it that for bikes it is soo "important" to check the valves. Anyone that owns a car never has valve checked, ppl drive their car, do oil change and thats it... Put on 200,000+ km etc and never worry about it. I know the bikes rev alot higher than cars, but still the dealerships make it seam like ure engine is gona blow if you dont do it. Wouldnt it only cause a problem if they tighten up?
The thing about bikes is, as you state, that they rev higher. A LOT HIGHER! This means that parts undergo much higher decelerations, which causes them to "stretch" (undergo elastic / plastic displacement) of a greater magnitude than cars.
Coupled together with the higher compression ratio, you have a much greater chance of your valve hitting the piston. The high compression ratio means that the piston is closer to the cylinder head at top dead centre. If your valve clearance is wrong... Klap, snap, grind... No more engine.
And yes, putting in good oil at a regular interval will make a difference. Loose the lubrication between the cam and the shim, and it will grind it away in no-time. This may lead to the valve hitting the head hard instead of gliding into its seat --> Throw away the cylinder head or get it reseated and new valves put in.
A few bucks every few ten thousand km spent checking the valves vs a thousand for a new engine? I know which I'm choosing...