I have that same 'malady' Keith. It's hard to break the habit of checking Ebay for instruments I certainly have enough of and no longer need to keep buying. And it really is just a habit... I can't stand the idea that I might miss something wonderful... despite having enough wonderful examples already.
This is true for some various instruments I own or play... not just penny whistles. It seems I have finally broken my need to seek more whistles though. I've disabled a few of the 'saved searches' I've set up on ebay over the years- that seems to be the key to breaking the habit, for me anyway.
Those irritated by grain of sand best avoid beach.
-Strumelia proverb c.1990