Just lock Dawn in a cupboard for the entire season and make the nerds do something a bit more extreme. I know the entire point was for them to be lame but it wasn't quite lame enough for me, would have preferred it properly lame or a bit more hardcore. Also a better build up to Xander walking out on the wedding, I felt that it was built up certainly but still seemed a bit random by leaving it until the very last minute.
Saying all that though, season 6 is still my favourite season.