UPGRADE! UPGRADE! UPGRADE!
If you are a Premier or AE user, the integration is simply amazing in CS6. They have fixed so many problems!
We used to ONLY use Final Cut Pro 7, and when FCPX came out, we didn't want to switch (I don't like FCPX at all).
We use Nuke, Maya and After Effects and were starting to have problems with FCP7 and it's ability to import/export/play nice with these other programs.
Once CS6 came out, it was a whole new world! Everything is an improvement over CS5.5 and it's light years ahead in speed compared to CS4 and makes CS3 cry.
CS6 features the Mercury Playback Engine and it is just amazing for speed.
Renders that would take me 2 hours in FCP7 only take 15 minutes using CS6 on the same machine!
If you can afford it, it is worth every penny!
It will save you so much time!