If its just occasional track use, a set of track pads would do the job. Plenty will fit the oem caliper. Just look at the tracking forum to get ideas in which ones to get.
To answer your question , a bbk may not necessarily equate to improved braking performance. Improved resistance to fading - yes. If course better resistance to fade means you can get on the picks hard more often but absolute stopping distance may not be significantly better. I've found that the main factor in how late you can brake is the size of your testicles.
As for the value equation, well that's up to you. There are plenty of guys with bbks who never intend to see the track but will attest to the value of a bbk.
There a plenty of guys who know much much more on this than I do on the suspension , brakes and chassis forum and I'm happy to be corrected by them.