I've got Mixcraft Pro Studio 6 -- what additional plugins would I get with Mixcraft Pro Studio 7?

Here are the plugins that you get in addition to the 19 that come with Mixcraft Pro Studio 6:

ME80 Version 2
Glass Viper
Fusion Field Convolution Reverb
SideKick6 Sidechaining Compressor
Studio Devil Virtual Bass Amp
Dubshox Multiband Distortion
Treblecream
TRW-1 Vacuum Tube Triode Warmer
VTC-1 Vacuum Tube Compressor
POD4500 Particle Delay
PSEQ-1 Vacuum Tube Passive EQ
VBE-1 Vacuum Tube Bass Enhancer
Zener Limiter LM-2Z

Here's a chart that shows what you get with the different versions of Mixcraft 9: Mixcraft Comparison Chart.