S13 CA18DE, CA18DET and SR20DE brakes are all the same. Front brakes are bigger on SR20DET models(rear still the same).
The CA - SR brake upgrade is definitely worthwhile! Made a big difference on my car. Was relatively cheap too.
250 - 280mm disc upgrade, with bigger calipers and pads.
Mine cost me $200 for the calipers and freshly machined discs (off of here actually). Even got some used pads, but chucked em out and spent $150 on EBC greens (these are good, but go with whatever brand suits you - there's a sticky on this)
If you're reasonable handy mechanically you could do it yourself, it's a relatively straighforward job.