A couple of things.
First, my (unfortunately now a bit dated) personal map for shore diving sites on Cayman Brac: http://www.huntzinger.com/dive/brac/brac-shorediving.html
Second, I'm going to agree with asmith2
's comment about declining reef conditions on Little Cayman's north side, specifically in the famous marine park. One of these years, I'm going to digitize and post a longitudinal study of those reef's health ... if I get to it within the next five years, I'll have had 30 years worth of photographic data. The blunt reality is that these moorings have never had any fallow rest period since Paul & Donna Ingles put them decades ago while working for Gladys Howard, and they're being loved to death.
I kinda have to disagree with you in some ways. Yes, there is some stunning diving on LC, especially Bloody Bay, but in the last few years, most of the shallower places on the north side seem, in my opinion, to be a little beat up. There are far more dive boats competeing for sites on LC. The walls on Brac offer diving that's just as spectacular, although perhaps not offering as good an interesting shallow water safety stop depth. That all being said I'm looking forward to being in LC next week.
A nice comparison; what many divers love about LC's northside marine park dive sites is that they're so shallow, which allows for long dives. This also makes them quite excellent to also snorkel too. Whereas most Brac wall dives are typically ~60ft to the top of the wall, which isn't good for snorkeling, plus it makes for shorter /deeper dives. For shallow reef dives, the Brac is quite comparable to Little ... better, if you like Spur & Groove formations, as LC's northside is more akin to spot reefs (when it isn't so shallow that it is literally just hardpan).
And while some folks really like LC's sheer wall sites (such as Great Wall West), from an UW photographic interest perspective, "Big and Flat" is actually quite limiting. These walls are also in shadow, since they're northside walls - - that can be good for UW photographers composing sunball backgrounds, but not so good for non-photographers. As such, they might prefer a dive on the plunging southside walls of Cayman Brac fully lit up in the sunshine...
...and when it comes to canyons and swim-throughs - - particularly if you like a large amount vertical relief - - while there is some nice stuff, particularly in LC's Jackson's Bight area, there's IMO more of it on the Brac and overall, a bit more satisfying. Case in point, Paul's Anchors doesn't have anything like the Brac's Anchor Wall: http://www.huntzinger.com/gallery/index.php/Brac/IMG_6095-anchor