The Grand Place is certainly worth seeing, not so much the Mannequin Pis. You'll certainly be able to get a croissant and a coffee, not so sure about beer. I've been though BRU twice since the attacks and noticed no difference, but can't speak to US departures. However, elsewhere in Europe, US departures require 2 hours and, although there are lots of signs warning of increased security, I haven't come across physical evidence of any increased security. You still get asked the silly questions by untrained people and you still go through the general security lines.