I wouldn't judge autocross as critically as tracking. Think you're fine on that event.
I very much understand, that spending 700 $ on directionally vented discs is a huge
hurdle. I've been aware of this when I did my last post. Nonetheless (from guessing)
I'd think directional ventilation is capable of decreasing rotor and pad peak temps by
100° F or even more.
Removing shields + fitting TT-RS (which require some modification to them) is the
most cost-effective way. Fitting hose is better, but much more complicated. If I do
remember correctly, forum member 'Maody' has performed that on his R:
http://forums.vwvortex.com/showthread.php?6946721-Maodys-Golf-VII-R
IMHO after one year and 15 kmls of street driving only your RBF600 (which is excellent
stuff) commonly shouldn't be too old, though several track days certainly are 'too much'
for it. I'd swap brake fluid after any or every two track days, as brake fluid detoriates
rather quickly when that hot.
As mentioned, boiling fluid says much about the temperature of the entire brake assembly.
When the fluid boils, it does boil because the pistons get hot (or even hotter). When the
pistons get hot, the seals also get hot.
While you perhaps could solve that issue by swapping more often or using an even more
advanced fluid like Endless RF650, it would do nothing on other problem areas, of which
the most significant is your caliper seals. That said, from my own experience the very
most underrated single point when it comes to brakes and tracking is ventilation.
In other words, it's a darned good idea that you're going to improve the ventilation.
Lastly, yes, brake assist setting is a point on any Mk.VII. Take a couple of hours and
try all of the settings (if I remember right, there are three). I'm sure you'll notice the
difference when you jump onto the pedal. The most natural feeling setting is ideal for
track.
.