It's not a load of crap son. I'd do mine every 10-15k to keep on top of maintenance, to make sure she's running as best she can with high compression. F00k knows what your compression must be like if you've got the same piston in after 30k+ miles lol or you might just ride like a granny ;)
there's no rattling on mine even at almost 30k miles, so clearly is a load of crap ''son''. when there's rattling i will do a piston change, why bother when you don't need to. it hits 75+ so clearly nothing wrong.
Just because you've got no rattling doesn't mean that your compression is lower than it could be with a new top end :)
And it isn't a load of crap, it's good peace of mind knowing that your top end is maintained at good intervals.
You could run the risk of your old 30k+ piston shattering all of a sudden because it's so old and over used! Then you'd have a fun time getting all the piston out of your bottom end and having chunks msising out of your liner.
Each to their own though bud, but me personally for the sake of a few quid i'd do it after such a long period of time, it's not particularly expensive if you think about it, even if you did it once a year!
Just got my spare barrel back from a rebore and for the piston kit, small end and rebore it came to 90 quid.