I haven't gone to a Villains After Hours event but I did go to a generic Disney After Hours event at the Magic Kingdom a couple of years ago. The waits were ridiculously short and I was able to do all the things that I wouldn't normally do, such as the Astro Orbitor and Princess meet & greets. If you want to wander about in a park that's less crowded than the holiday parties, then definitely go. Here's a description of the Villains event from Undercover Tourist.
