You would want all or nothing in a momentum class like TAG for front brakes IMO. The driving line and braking points are too different to not have inadvertant crashing like we had in the 80 shifter class. Especially at the end of long straights like IMI & GJ.
I would think the $700.00 adder would be the deal breaker. And not having ever raced in TAG or ICA, do front brakes limit the amount of trail braking you can do to keep the momentum up? I always thought that was the fast way around the track in TAG.