Somewhere in between those 2 answers is probably the truth
Between my group of friends we've had a DL1000 (mine), 4 SV650s and an SFV650 Gladys.
All had valve clearances done at beyond the interval (20k(ish) for the 650s and most likely 32k for my DL1000, although I don't know for certain they were skipped at 15k, I just suspect it very strongly.
All were within tolerance so didn't 'need' adjusting, I only changed mine as they were close to or on the limit and the tear down is more work than the adjustment on the 1000cc.
Overly tight valves (they tighten with wear rather than loosen) will stay open past when they should be closed and this can cause them to let by. The exhaust (the one that suffers most) will pit and burn away at the valve seat which is the head damage mentioned, adjusting the valves too late will mean they won't then seal correctly on the damaged seat. The intake staying open will lose compression and therefore power but the seat is less likely to be phyiscally burned away.
Regards DIY, checking them yourself is not that risky as you aren't changing anything, it's only once you have to remove the timing chains to adjust the gaps that the risk comes in, re-assembling with the timing fractionally out will cause the engine to run super rough, out a long way and that's potentially engine over. It's entirely dependant on your personal level of spannering ability but I did mine having never tried valves before and it was fine as long as I was very methodical and followed each step to the letter whilst taking plenty of notes. I have rebuilt simpler engines (stationary singles etc) in my time though so wasn't going in completely blind.
* My friend had her Gladys done this month and the cost was really not that big. For peace of mind and service record on a bike you think is a keeper, it's your call.