Do it! If there's even a possibility that you'd go back, it's totally worth it. Even if you just plan to go next year around the same time. We did our first ever APs after our September trip last year. My DH decided it before we went and had to talk me into it b/c I'm a cheapskate. We've ended up doing short trips in Dec, January, Spring Break, and for our anniversary in June, and will be ending our APs with another big week trip in September. We plan to take a year off and then maybe get them again next September. It's kinda freeing to be "obligated" to go to Disney and get our money's worth out of them. I don't see us doing it every year, but it is nice to be able to go in on your arrival and leave day without using a whole day's ticket or "wasting" money. We've been several times after I get off at noon on Friday and made it in time for the fireworks! We've found a great off-site place to stay so we don't break the bank.
Again, I don't think we'll ever be continuous passholders, but getting 2 yearly trips out of one saves you money AND gives some flexibility to go back on a whim. Not to mention the 20% merch discount, a few food places, and the magnets. LOL