If you're able to, I'd recommend going both days. There's definitely a lot to take in. You can walk the floor 3 times & there's still plenty you would have missed.
A good deal to someone might be just a regular LFS price for someone else. I always like seeing stuff that you just don't see every day. So you definitely see plenty of that on Saturday. Plus factor in all the non coral vendors if you wanted to check that all out. Sunday can be the 'deal' day if you're going solely to look for cheaper coral.