There have been several really good ideas posted in the last month. But I think that the eventual consensus each time was that as long as USASF continues to make a profit on every team that participates, bids will never be limited.
How about a pre-Worlds event on a different weekend, where everyone with an At Large bid has to compete to qualify for Finals? USASF can rake in the cash on two weekends, and it might discourage teams from taking a bid "just for the experience".
I am only half-joking about this.