Swop out your fluid for starters.
Decent fluid, lines and pads are critical.
Expensive rotors and BBK should really not be required for your applications.
Proper bed in + warm up laps + cool down laps is a given every time you go on / off track.
It is amazing how, when you feel the pedal getting a bit soft, say after 8 laps, that a couple of proper cool down laps bring the temps right back into check.
However if you are expecting endurance type of brake efficiency then you will have to think again.