AGREE wholeheartedly with TIW- it would be silly not to invest if you have an AP. If you think you'll be there often enough to make AP worthwhile, you'll be there enough to make TIW worthwhile. (even just 7 days a year, sometimes it's a bad year, and i only go for 7 days, but get the AP anyway, because of the savings with room discounts, TIW and purchase discounts, and it still pays off). remember only one member in your party needs an AP for everyone to get the discounts.
One dinner at Victoria and Albert's with my daughter and son in law and it more than paid me back the $75, i considered the rest of the discounts pure profit. it's made us finally able to pull the trigger and say- let's go to V&A, hey, it's 20% off!
just be careful, the TIW membership begins when you buy it, not when you first use it. and it takes 4-6 weeks (or so they say) from the time you order it online or phone until you get it.
as long as you have to stop at a guest services to activate the AP, be sure to buy it then, not to be tempted to get it ahead, and check one more thing off the to-do list, like i like to do.