in my opinion, mixed genre gigs dont usually work out. say all you want about opening peoples minds to other genres or whatever, but what usually happens is that when a metal band plays, the punk crowd leaves,goes to eat,or starts trouble and vice versa. replace "metal" and "punk" with whatever genre you want.
im not saying its completely bad, there were many occasions where mixed genre gigs made me aware of pretty good bands i wouldnt have known about otherwise, but sadly alot of people's minds remain closed.