We did it in 2002 and it was busier than I expected. However we got our timing completely wrong and arrived at the park about 7 (I think) which was when everyone else was arriving. Next time I would make sure I was in MK that afternoon and stay for the changeover period so that you get first go when the park re opens for the night. Also, it started to thin out about 10.0pm but then there was a downpour and we ended up leaving. All in all had a good time but it wasn't a case of "walk-ons".