It'll all be down to the weather. People just don't want to leave there house at the moment, so the park will be suffering and need to get people in. Cutting prices is a way to do that. Do Drayton normally do 2-4-1 vouchers? If so, then this is no cheaper.
That "rainy day guarantee" should get a few people through the gates as well, though most of the poor bastards won't have read the terms and conditions and realised what a non-offer it actually is.