Just a thought but we've been a couple of times and I would recommend paying extra (£5 from memory) to park in the area closest to the entrance. The first time we went it was dark when we came out and it was no fun wandering up and down pressing the remote for the car hoping to see our lights come on. It's also a lot quicker to get out, they had a priority scheme running when we did it last year.
I agree with taking your own food, it seemed expensive and the queues for food and seats were dreadful.
Apart from that we've had a great time whenever we've been We've never paid, Tesco do a good scheme where you get points for your shopping which can be exchanged for entry vouchers.
Hope you all have a good time,