I gotta say that the stretcher in 2001 made the biggest impact in FIRST, over everything else.
OK, seriously, I agree that the onset of alliances in '99 was huge. The concept of competing with a random partner and then picking alliances for the finals forced teams to work together. Teams developed better marketing and salesmanship skills and had to be accountable to other teams for the way they played the game. This raised the level of GP dramatically.
Andy B.