I think it depends on the event to be honest. There are some which I find odd, and there's others that appeal.
Last year, I went to London on one of their adult only nights and I thought it would be a lot of people just observing animals and I thought it would be a relaxed event. What it turned out, was a lot of people at pop up bars, listening to music, and a lot of over crowding. I didn't enjoy it, as much as I hoped I would.
However, this week, I visited Howletts and paid to do the after hours tour, where between 6pm and 8pm, a group of 6 of us, got to walk around the Zoo with a couple of the education team, and got to see the animals in a different light, as well as feeding a few around the park, which was thoroughly enjoyable. The animals were not disturbed and it ended at 8pm, so it wasn't late, and for most of the animals, it was only giving them their evening feeds that they would normally get. I found it thoroughly enjoyable, and for me, this was an example of how opening after hours was done right.