The Jaguar update offers new features that are useful to some very specific sections of the market, such as people who will be networking their macs. Developers will also get a lot of new goodies, and ditto for those running servers.
However, if you are really only using your mac to run a few specific apps such as Office or PhotoShop, and you are pretty happy with your setup now, all Jaguar really offers is a few (admittedly very good) interface tweaks and a speed boost.
So, I guess it depends on what you're using it for.