I too was at Brussels last weekend. It was my first time there and the wife surprised me with a trip. Full disclosure: I ended up going home with several hundred dollars worth of material.
This is my few cents worth of the trip:
1. Most of the stuff, particularly the beginner stuff, seemed overpriced. I couldn't believe my eyes walking through the tropical greenhouses what some of the price tags were on what is essentially a 1-yr old cutting stuck in a pot (particularly the p. afra). That said, I think of it as most practitioners, except for the very most green or someone trying a new species, aren't going to buy one of those trees. They will be looking for more advanced material, so Brussels is trying to make their money on the 1-time sales without effecting their repeat customer base too much.
2. As you moved up into nicer and nicer trees the prices would normalize until the point I actually thought there were not terrible price tags on some of the specimen trees. I didn't have that kind of money to throw around, but based on the time, effort, and input costs it takes to make some of those they were priced reasonably well.
3. There were deals to be had if you looked around hard enough. There were some decent black pines for 40 bucks...many of them were grotesque...utilizing the wire scarring method to get girthier trunks. However, if you dug a bit you could find some really nice ones 2-3" base with an abundance of low branching. Matt was telling several people he sells them on eBay for 3x as much. In the field of maples section, there were some excellent tridents with 3-4" nebari for 75 bucks. In the JM section there was bizarre pricing. One sitting right next to another could vary as much as $300 between the two....all else appearing equal. Not sure if it was a mistake that one just didn't get an updated price tag or what. I took one of these home for the lower price.
4. For commonly used bonsai specimens you can almost assuredly find a tree of that species there. For less common varieties, you almost certainly can not. For example, I was looking for a Linden and stewartia. I couldn't find either. Yet there were several cultivars (Arakawa, Koto Hime, Red leaf, green leaf, shishigashira etc.) of Japanese maple.
5. This is more like a corporation than a typical nursery/bonsai nursery. Volume and selection-wise...think of it like the Walmart of bonsai. The people are extremely helpful, friendly, and hospitable though. Every single person working there was great. They provided donuts, pastries and other things for breakfast along with sandwich wraps, chips, and pizza for lunch. Was really fun to sit around and talk with Brussel, other patrons, and the staff.
6. Plan several hours to walk around and enjoy looking through everything. Bring a stack of cash, like going to a casino and promise yourself you will not spend more than you took with you.
All said and done it was a nice trip. I prefer collecting/developing material more than purchasing but I think I will be back in a few years time.