Hi KCmike,
If you know you will be going back for that 3 day trip, then it makes sense to get the AP. Current prices are as follows:
3 day hopper: $214, $198 (child)
5 day hopper: $246, $226 (child)
Deluxe: $379 (adult and child)
Premium: $499 (adult and child)
You know those prices will go up, probably before summer with the coming of Carsland. If you upgrade from tickets, you will only get credit for what you actually paid for the tickets, so buying ahead cheaper and choosing to upgrade to APs after a price increase will not save you money. You could buy AP vouchers ahead of the price increase (once you hear that the increase is coming) but then will not be able to take advantage of Magic Morning first. Is Magic Morning worth extra money to you?
So the things to consider are whether you want early entry and if either of your trips will include block out days. Many of our trips include Saturdays or holidays, so we always just buy premium these days. Since we at least live in California and are willing to tolerate the looong car ride multiple times a year, we go four to six times with each set of APs, so it is worth it to us.
As suggested, you can always start with your tickets, use your early entry, then upgrade. You will want to upgrade as early in the trip as possible in order to take advantage of the discounts. If Al Lutz is right about those AP early entry days at DCA, you then might be able to do one of those too after you upgrade. I'm hoping he's right about those because that would work really well for us if we make it down this summer.
Deluxe AP holders receive a 10% discount at most food locations, 10% discount at most merchandise locations (until 12/31/12, not yet known if this discount will be extended again but it has been repeatedly over the last couple of years), and 10% discount at many DtD locations.
Premium AP holders receive a 15% discount at most food locations, 20% discount at most merchandise locations (until 12/31/12, see above comment), and 10% discount at many DtD locations. Premiums also get free parking. We rarely use this benefit as we generally choose to stay within walking distance.
Passholders can also get 20% discounts off tours, but you already have access to this benefit with your Disney Visa. There are discounts off the resort hotels as well, but, frankly, the one recent time we stayed on property, the public deal was better than the AP deal anyway.
So it all comes down to numbers and how sure you are that you're going to get that second trip in within one year of the first trip. Hope some of this helped.