Hello,
A few things to consider.
The benefits of The Dolphin are the location between Epcot & MGM, and the fact you don't need to wait on bus lines for either park. You can walk to either, or take a boat, which is a nice ride either way. You also can stroll the Boardwalk at night without having to worry about transportation back to a resort. You didn't say if you'll have a car on this trip, so if you don't this is a big plus. You could possibly end up with a fantastic view from your room, although it is not guaranteed. There are also numerous eateries in close proximity, between BW, Y&BC, and the Swan & Dolphin, that are easily accesible by foot.
The drawbacks of the Dolphin ( in my opinion) are the lack of Disney themeing, and the atmosphere is more of a generic corporate hotel. The grotto pool is DEFINITELY NOT heated, as another poster posted. You can not use your room key for WDW charges, outside of the Swan & Dolphin.
The benefits of CBR, are of course you save a few hundred clams on the price. You have Disney themeing and atmosphere. You have Disney charging priviledges. You have nice sized rooms for a moderate.
The drawbacks are (again, in my opinion) : If you are dependent on Disney transportation, the CBR busses always seem to have the longest lines, and you are limited in your destinations outside of parks, without making time consuming transfers. You have a limited restaurant selection at CBR. You could conceivably end up on the far side of the beach, which is quite a hike to main buildings.
Hope that helps,
Take care,
Bill