Last year whilst shopping for a birthday present for my dad, I took a chance on some ex-display headphones that were on sale at my local Richer Sounds. Up until then the best pair of 'phones I owned were some AKG-512 closed headphones. Otherwise I used a parade of low-end Sennheiser or Sony in-ear buds for listening on the move. The AKGs were a slight upgrade on the in-ear buds, but not much. They were noticeably bassier. Whether that was an improvement or not was up for debate.
The Sennheiser HD438s are quite an upgrade on the AKGs. It's the biggest improvement I've ever heard when listening to my music. It's the first time I've ever noticed a significant improvement using different headphones, confirming that my ears are good enough to benefit from better equipment. Until then I simply wasn't sure.
This goes to show that my existing equipment is not that great. No surprises there, but my lifestyle at the moment doesn't really have any room in it for anything better. I'm also glad I've amassed a nice music collection and discovered so much that I enjoy listening to before investing in the equipment with which to listen: I've heard new things in all my old favourites these these 'phones. Perhaps I will with a future upgrade, too.