Do you *need* the new features introduced after your version? Then get it. If not, don't!
I recently upgraded from 7 to 9, and apart from trying out the new functions I haven't really used them... but don't forget it also allows you to update to newer versions of their raw converter so if you use raw, the recent versions have improved compared to the past.
_________________Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.