I'm not ready to start throwing money at the car yet. I do think caliper flex is part of the issue and have an idea or two about that. I'll wait to hear from wilwood and Dave to get there take on things.
I don't understand floating rotors enough to get how they would help with caliper flex. I do understand how that design would greatly reduce rotor wear.
This is an interesting read on caliper design.
http://www.stoptech.com/tech_info/wp_monobloc.shtml
The search continues for a fast, reliable, cheap track car.
Perhaps perpetual motion would be an easier problem to solve.