While guys may get sticker shock from seeing prices like the Whoa kits, you need to look at what you get and your overall cost.
On my old 240Z, the brakes are questionably adequate to begin with.
My friends car has close to stock brakes and they really should have done a rear adjustment and bled the brakes after Saturday. They were losing pedal on Sunday most likely do to the wheel cylinders getting out of adjustment. The guys running the 260Z at MSR also had brake issues which were probably from the rear brakes.
I upgraded my car to 4 wheel discs with vented front rotors. It did cost more than a complete stock replacement but only by like $150. I have participated in 4 races and my brakes have been consistent through each race and all the races combined. My brakes can easily handle a full 24 hour race. They are limited by the tires and are a bit aggressive.
My friend's car would most likely need to be adjusted mid-race or several times if he runs a true 24 hour race. Old Zs don't have the best brakes to start with.
A drawback to my system is my front caliper. I run 280ZX calipers which pretty much limits me to Porterfield pads at around $100-125 a set. I think Willwoods use a more generic pad and they are less expensive, like $60 a set.
So sometimes a larger hardware cost will lead to a lower overall operating cost.
An even simpler example of this is running say Premium Pads from your local parts house versus a Race/track pad from someone like Hawk or Porterfield.
Your premium pad may only cost $50 a set while a Race/track pad may be say $80+. The race pad will probably last several times longer than a Premium pad. So say your $50 Premium pad is good for 1 race where the Race pad is good for 2 races. The Race pad is $40 a race where the cheaper Premium pad is $50 a race. So in the end a Race pad may be cheaper and safer overall.
The other problem is if you realize the Premium pad just isn't good enough and then you have to upgrade to the Race pad. Now you are out $50 + $80 = $130 instead of just $80 in the first place. The extra $30 saved you $50.
If I would have spent a little more time and went with a 4 piston Toyota caliper up front, I would have better pad availability which would have been less expensive. I still may go to 4 pistons in the future.
1973 Datsun 240Z