The park really has three options here as I see it:
Increase capacity by opening Forest of Fun (rides and Christmas overlay), Land of the Dragons (lower level only as a children's holiday village area), Festhaus Park (with the old planned Rudolph villiage concept), and/or additional rides (Alpengeist, Griffon, Tempesto, Europe in the Air, DarKastle). The main drawback to this approach is increased operating and staffing costs which make the potential of slower nights more risky to the park.
Alternatively, it may be time to seriously start pricing people out of the event. Go to a tiered, pick-a-day-in-advance pricing structure with Saturdays being the most expensive and weekdays being the least. The con to this method is that the park will have to accept lower attendance numbers and probably less profit made off of food, drink, and merchandising. Obvious pro is increased profit from ticket sales. I don't know that it ends up balancing out though.
The last option I see is to go back to the old way of putting a hard stop on the capacity of the park and turning people away at the gate. The obvious downsides here are a lot of very angry potential customers and leaving money laying on the table.
The crowds are seriously overwhelming right now- cheap ticket day or not. I feel like we're on a real breaking point as far as crowds go. Guests who aren't in the know and don't know what they're doing arrive at five and have a miserable time because they literally can't move. Those aren't people who will turn into repeat customers.