^ you know, I have the same old Logitech optical mouse that I think I've used for the past 10-ish years. I've never needed a new one...
I really wasn't planning on upgrading my aging Microsoft 4000 mouse either, when by chance I happened upon an eBay auction for a terrific price (new). It really is an improvement and I'm very glad I did it (ergonomically, functionally speaking). If you ever find yourself near a computer store, stop on in and check out some of the mouse models they've got. You just might find that old Logitech mouse you've been using is starting to feel a little inadequate (seriously, there have been some great improvements over the past 10 years).