Funny, I just responded to a chat thread about AP upgrades, then saw this thread. 
As others said, I believe it can be worth it for less than 10 park days of trips, depends on variations in cost etc.
I created a Google Sheet a few years ago where you can enter the tickets you plan to buy in the next year and other expenses and it will help you see if the bottom line savings makes an AP worth it.
It is admittedly a busy spreadsheet, so you can find a video that goes through an example if needed, as well as a link to the sheet in my forum thread:
Often if you are on the borderline whether worth it for multiple APs, the discounts/perks by getting just a single AP in your party can be a beneficial alternate tactic.