If you're going from V6 to V6, the engine should be one of the last things you consider, I've driven both, the 3.6 is faster, but the growl and sound of the 3.5 makes it feel "faster".
The reasons you should get the new one:
-taillights, IMO, best in the world, nothing can beat them.
-suspension, especially with performance suspension and steering option, it out handles the older gen base r/t's IMO, I've driven both. It also feels planted yet the ride is composed.
-the refinement, something the older gen's were missing, the interior is great in the newer ones.
-sound deadening, the car just feels tighter, better put together and the interior is very calm
Get a hemi if you can, if not, I say go all out and get a 2012 blacktop fully loaded with the 8 speed transmission.