If someone in your party is likely to visit WDW for 8 or more days in a year, the AP is a great idea.
If they are going to visit 7 or less days, I would explore the discounts options available and make the decision based on how much (if any) money the AP discount would save over the DC or other available discounts (Currently, according to Mousesavers, you would save 30% on the room with AP compared with 15-20% with DC; at a Moderate that would be about 18 bucks a day savings).
Last fall, with our AP, we saved enough in about 3 nights (AKL concierge) to pay for 1 of our APs. However, we bought them because we were planning at least 2 trips to WDW, and they saved us $$ on park admission alone.
As far as other benefits to the AP, free parking at the parks might be attractive to someone who stays offsite, and I think there are some dining discounts (small), a newsletter, and some other small bennies.
To me, the biggest benefit is that if we can find a cheap last minute airfare to WDW, the APs can let us squeeze in an additional cheap trip to WDW!
