I just wrote a little about my experience in a mini review. I'm just back from a stay in Sierra with a DTD view. I thought it was absolutely necessary to have that tower and view, but you know what....I like my city view in Marina better. The Marina room was a lot larger, but I think it as just a big room and not indicitive of all rooms in Marina. The lobby was so much nicer and more exciting. I thought the DTD view would be "WOW" and it was more, oh wow. It wasn't nearly as interesting or neat as I'd expected it to be. I though access to the pool was easier from Sierra, but other than that, the distance to things didn't make much difference.
From photos I've seen, for that "WOW" view I was expecting, I should have stayed at PP with a theme park view.