Thanks guys, the opinion seems unanimous!
We were looking at a Little Mermaid room, and I know that I heard they were pretty far from the amenities... I guess it really comes down to that one night extra and the 1500$ savings for me. That water park is awesome, but the last 2 times we were in WDW in December it was pretty cool and rainy so not exactly pool weather for me. But the Christmas decorations at BC are so awesome...
I really loved being able to walk to Epcot, but with my two young ones I was thinking we were going to spend a lot more time in AK and MK so the close access to the other 2 parks while awesome was less of an issue. I'm also wondering how my youngest will fare on the walking front; she's a bit of a drama princess!

Last time we were in WDW my oldest was 5 and the youngest was 2, so the stroller was definitely a no brainer for us, and strollers on the bus are such a pain that access to the parks with minimal bussing was a priority.
Last time we were also staying on DVC points, while now it's all $$$, so that also makes a difference...
Maybe a split stay?
So confusing! But it's definitely a good problem to have!