The final image comes down your RAW Processing. I get great skin tones from any camera by getting the exposure correct and processing in LR3. Shooting at a larger aperture will provide the buttery background but your subject may not still have those nice skin tones.
Switching to FF will not magically fix your skin tones, Its your processing that will do that.
Any tips for getting the exposure correct?
The FF would help with crop factor and IQ moreso than actual skin and individual shots is what I meant. I'll have to download a trial of LR and see what I can accomplish with it...
Use spot meter on your 7D, and get the metering for your subjects skins tones first. Determine if its accurate by your histogram readings because darker or lighter skin tones will throw your meter off. Use that setting you determine and should be perfect skin tones, and if not, Process the RAWs to correct it in post.
Yes, FF is better than crop in every way but I still keep my 7D for strobist/sports/reach that it provides me. I believe you should reach the limits of your camera before deciding to purchase a much more expensive camera.