the march tickets no, the august yes. tickets can be converted & upgrade only if you have valid admission days remaining on them, which since they expire 14 days after first use, the march ones no longer do. the one thing i dont have to advice on is the value they assess tickets as part of a package, but i'm sure someone else could fill in that blank.
as far as financially, based on what you've said odds are, its definitely worth it. since you clearly stay on property, using the AP room only discount and then paying for the dining plan is often better than what you'd be getting with your free dining package, but your mileage may very. they also automatically include park hopper, which is a great added value if you use it, and the same could be said for memory maker. if you are even a moderate shopper, those discounts help justify the cost. i tend to advise people if they go to the parks more than 8 days a year, its with it.
my personal favorite perk is using it on arrival/departure days when I'm not getting a full day at the park. if i were on a regular ticket and my flight landed after, i dont know, 3pm, i dont know if i would do to the park because i wouldnt be getting full value for that day worth of my ticket. With my AP, i've literally landed after 8pm, checked into my hotel, gone to a park to watch fireworks, get on a handful of rides and then back to the resort.