Trust me, it won't be cheaper in the long run......they just burn a hole in your pocket....that itch to go back gets stronger and stronger by knowing you already have the passes!!!
LOL, I'm totally kidding, we've had them for a few years now.
Anyways- With a room only reservation (or with an AP discount) you won't be able to book a dining plan. The dining plan is only for MYW packages or DVC members (or renters) staying on DVC points.
You could book the MYW with dining plan and buy the 1 day park pass. When you get to WDW you can then upgrade your tickets (they'll credit you the 1 day cost) to the AP.