It's actually a fairly quick job to check them, not so much to adjust them. So, if you want peace of mind, just ask them to do it anyway, it's your cash.
If they tighten up, they will burn the valve out, because it's not closing properly, but this takes ages to happen and it would exhibit other symtoms before that. The way you can tell is a slight drop in power, or a hunting at idle, much like if the throttle bodies were out of sync. AFAIK it's nothing to do with the clatter you might be hearing. They rarely loosen up as far as I know.
My 99 Speed Triple went for 40,000km without a check (previous owner didn't get it done at 20,000) and exhibited no ill effects, but, when they were checked again at 60,000 they were quite out of spec, leading me to wonder if I had have had them checked earlier would they have been less out of spec than they were? I'm not a mechanical whizz really, but I do wonder. The S3 went on to do 110,000km before I sold it for the Tiger, and the valve clearances still had some left to go before a head overhaul would be required.
Mick
