I did MK After Hours last month! I think it can be worth it depending on your priorities. The day before AH, I asked in the My Disney Experience app chat feature which rides would be open for AH and they replied right away with a list of attractions. The only major attraction not on the list was Tiana’s, so I rode it another day. I was able to ride six rides between 10pm-1am, getting walk-ons for Space Mountain, Jungle Cruise, HM, and BTMRR, and 30-minute waits for 7DMT and Tron.
It was neat to stroll around the park without the crowds and strollers, and I was able to get a spot (for one person) in front of the castle for the 11pm fireworks only five minutes before it started.
Keep in mind that most shops and restaurants will be closed during AH. The only shop I remember being open was the one you have to exit through after Space Mountain. There were kiosks with popcorn, ice cream sandwiches/bars, and soda in cans.
Here’s my trip report if you want to read about my experience: