Depends on what you find yourself doing with it and if you're happy with the image quality. If you want widescreen, higher resolution and the smaller size, then upgrade. If you don't care about that stuff or just don't want to upgrade, then don't! Its old but there's absolutely no reason to get rid of it if you like it.
Personally I found myself running CRT screens for a lot longer than I wanted to, and I'm really happy I invested in a new monitor, but I know some people how absolutely swear by their CRTs too, so its a matter of to each their own I guess.