Well just got back from the Sunbelt Tour and I'll add in my impressions. First off I drove like butt...a bit worse than even my normal. Also I was on Hankook RS3s and they suck when its cold...and it was cold and I didn't have a codriver to get more heat in the tires. I couldn't figure out how to use the most of the car with the lack of grip. I did ok in the RTF class (2nd/5) but was well behind the pace I should have been. But it was my first major event and a it was a great learning experience. Weather was very un-Texas like - cold and misty on Saturday and then colder and windy on Sunday.
But pretending I drove as well as I could (I have a good metric knowing many people I regularly drive with) I would still it is pretty hard to imagine myself keeping up with the mini without A LOT more prep...and really there isn't any knob to tune other than add shocks. The mini is far more controllable, lighter, and doesn't pitch around like the sonic. I'll continue to autocross the Sonic but I probably won't be trying to prep it much further or push to hit anymore big events...need to work on my consistency first.
On the other hand, the event was a blast and I highly recommend getting involved and hitting some cones. I regularly surprise people with the Sonic and even if its not "the" car, that won't matter until you're a top driver.