Have it be during a slow season, offer day ticket upgrades and a low cost for night tickets ($30 max), and LIMIT TICKET QUANTITIES.
So you're proposing they have the Universal version of e-ticket nights?

I know with WDW, the enights are an additional $12, and they get plenty of takers, so something in the $10 range might be acceptable...I think much more than that and there wouldn't be enough takers, not in the slow season when everything really CAN get done during the day and lines aren't a problem.
I think if they had one night a week where they stayed open later and had fireworks (and by later, I mean, even 9, it's dark by then), it would make people very happy.
It seems like with Universal it's All or Nothing with the nighttime/fireworks thing.

Karen
