If everything you have works well enough for you right now, there may not be a compelling reason to update.
If you are experiencing problems (such as being unable to interact properly with some web sites due to the old version of Safari), then it might be a good move to upgrade.
But -- as Idefix suggested in reply #2 above, don't go all the way to Mavericks yet -- too many folks reporting problems.
I'd suggest 10.8 -- or even 10.7.
Also -- be aware that the latest version of iWork that was released with Mavericks seems to be somewhat "stripped down" feature-wise, from the versions that preceded it. I'm using Pages 4.0.4, and will not upgrade further, because if you use anything more recent than that with the newer versions of the OS, you lose the "Save As" choice in the menus. This may not bother you, but it certainly bothered me.
Something else to be aware of: If you are currently using any older apps that are "PowerPC code" only, they are not supported past Snow Leopard. The apps must be either Intel or "Universal binary" to run under 10.7, 10.8, etc. If you have Spotlight running, you can check this by going to Apple System Profiler, clicking the "applications" choice on the left, and then examining the results on the right (tip: click by "kind" to sort everything out).
One other thing. If you have an external backup drive (you should!), before you attempt a major upgrade, use either CarbonCopyCloner or SuperDuper to make a bootable clone of your main drive. That way, it's easy to "go back" if you don't like the results or encounter other problems.