Tbh mate, I would say the most cost effective upgrade you can do for your Gen 4 braking system is this;
1. Accord Type-R brake setup
2. 4 quality tyres
The ATR system is regarded as an excellent upgrade to the stock prelude setup as it features twin pot calipers & slightly larger discs. Then you can always upgrade the discs & pads with something like Black Diamond, for example, to complement the better calipers, if so desired.
Worth bleeding the brake fluid entirely as well, & replacing with new I reckon. Helps everything work at it's peak efficiency.
Then, in terms of tyres, the two I would be looking at would be;
a) Toyo Proxes R888
b) Uniroyal Rainsport2
The Toyo's are ultimately a track tyre, and as such are not ideally suited for everyday driving conditions imo. They are more expensive, will most likely wear out faster, and not perform quite so well in the wet (which is a major factor to consider in this country)! I've never tried them, but they are raved about on here by track goers, so they must be relatively special. I would have these solely as a spare set on 16" rims, to use for track days personally.
Then you have the Uniroyal's. These are also well regarded on here, and are a decent all-round performer. Great in both wet & dry conditions, fairly priced, and last pretty well. Have a nice tread pattern too!

You must get the hardened tyre wall version though. Apparently it's noticeably better. I have Rainsport 2's on the front of my Gen 3, and I have to say, they are excellent. Not sure if they are the uprated version or not though?

A solid choice for everyday driving imo.
There are of course, other options when it comes to tyres. These are just my two preferences at this moment in time. Until I have Pirelli P-Zero money, for example.
All in all, I don't think it's worth forking out for a 'big brake kit' or the like unless you're building an all-out track car. Plus, such a setup will probably perform worse than stock until warmed up, like you say. And how often are you likely to be benefitting from that on our roads anyway?
Best off going with the above setup I'd say, then Polybushing your ARB's & Stabi links, then upgrading your shocks & springs. All this should see you pretty good to start with.
Seriously though, TYRES! Replace all four of these first, then see where you are. These so often get overlooked or compromised on (by myself included in the past), but they are your only point of contact with the road. So they are fundamental to the way your car will accelerate, stop, and go round corners. None of these will ever be at their best without good rubber. You will surely be amazed at the difference in stopping distance from doing this alone.
Arguably the most beneficial upgrade you can do to improve your car's performance.
And finally, it has to be said, for best gains the 18" rims aren't doing you any favours!

Trade in for some 17's for everyday use, & get it lowered.
p.s. Give this a read. Good relevant article:
http://www.preludeonline.com/f28/big-br ... de-248561/
Hope that helps a bit.