I have 4 discs brakes too and it's pretty nice. Front are genuine VW parts and rear from a Golf 3, master cylinder have a bigger diameter, it's the one they call "Cup". To be more powerful you can put Simca 1000/1100 calipers on the front, they are plug and play on the vw spindle, and the interest is that you can put soft or ferodo pads on it.
If you're locking the front wheels, you can try to use a bigger cylinder on the rear wheels to help compensate for the small tires & rake.
As Yvre says, on a beetle it's better to have more power on the rear brakes than on front-engined cars to equilibrate the braking.
About kits, I heard CSP are good products, but I never had the opportunity to try a car with it.