We usually have 2 trips a year, the January trip between 7 & 10 days, and August trip between 12& 14 days so an AP pays off with park admission.
We do go at times that an AP discount may be offered, but with dwindling discounts they aren't what they used to be. Also we have gotten the Premium AP to include water parks, and the merchandise discount was 20%, but now it is 10%. You get some discounts on restaurants (if you eat on a Thursday between 1:00 & 1:30

), well, not quite that bad, but there are different restrictions on each, and it is kinda hard to keep track of them
Last year we split the TIW with a friend, I forgot what the break even point was before you realized any discount. I think it was somewhere between $375?
This yeat the TIW cost went up a considerable amount to $100, from $75

so we'll have to re-evaluate if its still worth it.
You can upgrade your tickets at any customer service kiosk in front of the parks, or in DTD. Be sure to have photo IDs with you.