Extra Magic Hours are for guests staying at WDW resorts. They have nothing to do with the type of park ticket you have, nor whether they're linked to your KTTW card. The only advantage to having your park passes added to your KTTW cards is that it's one less card to carry around. If you get a CM (Cast Member: Disney's term for its employees) who knows how to do it, all well and good, otherwise, why worry? With the introduction of MagicBands, both passes and KTTW cards will soon be defunct anyway.
Regardless of whether or not we think we'll visit again within 12 months, we always buy APs for a number of reasons. (1) We tend to visit for more than 14 days (normally around 18). (2) Annual Passholders receive discounts and perks. In the past we've taken advantage of passholder previews of Soarin' and Expedition Everest before they were open to the general public. Admittedly, these perks are now available to DVC members, too (last November we were lucky enough to get a member preview of New Fantasyland). (3) Even if we don't think we're likely to take another trip within 12 months, we'd be kicking ourselves if we were suddenly in a position to do so. (Bear in mind that even if you only plan to visit once a year, there is still the opportunity to use your passes across 2 trips. If you intend to visit for 2 weeks at a time, you only need to move your dates forward by a fortnight in the second year to take advantage.) (4) As an Annual Passholder you're entitled to purchase the Tables in Wonderland card which gives a 20% discount on food and beverages (including alcohol) at virtually all Table Service eateries property wide.