I strongly suggest against using medium density fiberboard for the walls of the maze; it does not work that well and the price for pine is only slightly higher. Drilling holes for the wood dowels tends to destroy the structural integrity of the MDF and there is no way to route the edges of the walls to join them. I would definitely paint the floor of the maze black next time and use white electrical tape for the line following portion of the challenge. Black lines on white worked well but the floor of the maze tends to get dirty.
Building the maze in accordance with the micromouse specifications allows the maze to be used for multiple contests. The Lego NXT robots seem to work best with about twice the width between the walls, so just leave out every other micromouse wall.
The NXT-G Programming language worked fairly well until some student's algorithms become too complicated. At the end some groups were constantly running out of memory and having issues broken myblocks and unconnected wires and elements. However for the majority of students without a programming background the NXT-G programming language was much easier to use then anything else despite its limitations. The biggest problem with using the lego NXT sets for a robotics class is that the students consider them toys so they initially underestimate the challenges ahead of them.