Well, the ugly blunt truth is that you probably won't miss much aside from specific CoDec support for some newer formats. Pretty much everything is a matter of "unless you have specific workflows that involve those tools, you may not care", meaning things like Refine Edges, the content aware scaling/ resize, refinements to the 3D tracker and Warp Stabilizer, mask tracker and a few other things. Everything else is too much in a state of flux to really add genuine production value, the many quirks and bugs will drive you insane at times and of course some features like the motion graphics templates are downright irrelevant if you don't have those projects where you need to churn out hundreds of lower thirds for editing in Premiere. Sadly, AE is just stuck in limbo and seems to move forward at snail pace, if at all these days. Too many grand promises that it doesn't live up to. Other than that of course one might be concerned about compatibility issues with CS6 on modern operating systems, which is something you should really research thoroughly.
Mylenium