Another positive vote for Swan/Dolphin. We loved the proximity to all of the non-resort restaurants and preferred walking to Epcot and Hollywood Studios (generally quicker than the boat). Bed is much more comfortable than Disney resorts. Biggest drawback vs Disney hotels is no magical express from airport (and parking is expensive). Great value vs Disney resorts.

SPG Platinum doesn't get you much (no club lounge); we were upgraded to a corner room (no suite) with slightly more space and given some coupons at check in. Continental breakfast is free, and upgrade to full buffet is $7-8 (although one of the free breakfasts is a character breakfast). I wouldn't recommend any extra work to attain platinum status before your stay.

Personally, we would avoid WDW during spring break at all costs. The tip on the dining situation during busy seasons is great advice. Another tip (and another reason we liked Swan/Dolphin with walking access to two of the four parks) is to avoid the buses if at all possible. It always amazes me how much a family spends per waking hour on a Disney vacation, and then how many waking hours they spend lining up for and riding the miserable buses.