+1 for this function. Something similar to the pic above would be excellent. Or the 'performance' and 'studio' mode idea. Either way would be some attemp at trying to use the controller MORE. I modified the Hanz Apc Ableton Script for my Spark and use it(the Spark in midi mode) to launch clip recordings and patterns at/from the spark more than i use it as its own vst controller. I just jump midi/vst mode back and forth as needed, Making clips then launching and effecting.
On this note it'd be smoother sailing during performances if the controller sent a 'connect' message out to the vst when you switched out of midi mode. That way you wouldn't have to click the connect button in the vst to 'reconnect' the controller with the program. A sort of 'auto detect- reconnect' function.