There is an attention to detail that you find in Disney Resorts that you just don't get in the S/D. The decor is very authentic, thought out, and the hidden Mickey's are everywhere. The S/D are nice properties, but they really are just very colorful hotels - there is not thought to themeing.
Also, I find the serivce better at the Disney hotels. The S/D service is actually very good, so Disney's is even better! At least with my visits, I've found the CMs very eager to help and assure us a pleasant stay.
Oh, and of course, there ae the terrific Disney pools, which another poster mentioned.
Unless you are getting a terrific rate at the S/D, I would stay at a Disney property.
Nicole