Why not add another nephalem valor type buff for each additional person who joins the game? When 2 people party up, they could each get a 25% boost to experience, magic find, and gold find, maybe even a small boost to pickup radius as well. Add another 25% boost per player after that, so 3 players each get 50% Exp/GF/MF, and 4 players would get a 75% boost to Exp/GF/MF. People would actually consider playing together and farming together because they could get double the NV 5 stack bonus. Good teams could benefit a lot from this, and the game would be more social.
aside from that, if it would be possible to make joining brawling games more easily that would be great, randomly joining a1 pubs over and over until you find one where the players are brawling is just terrible.