We don't regularly grow cauliflower here because our season is too short, but I'll chime in a +1 on row cover for brassicas. I am old enough to remember growing broccoli without it - my Dad was really determined to have it every year and while he made nice heads, the number of caterpillars we consumed over the years was...
Those little suckers are bitter! The only save is that they change color when steamed so you have a better chance to pick em off your plate.
The organic brassicas including broccoli at my friend's farm are immaculate - only thanks to the row cover. It is really a miracle product for organic growing.
Kale and other brassica greens are only covered until they get started, so BT is still required from time to time. Rotation does make a difference! The worst infest is always where you sowed brassicas two years in a row...