We did not have Starbucks coffee packets during our last stay there, but that was almost 3 years ago, so perhaps a more recent visitor could post....the coffee was in Picabu's ( formerly Tubbi's) I do find the food fairly expensive at the S/D...we like to hit the Boardwalk Bakery as you can have sandwiches made and carry those to the park...they are large enough for us to split....ESPN is not a bad deal either or ordering a quick pizza.
The walk to MGM is not short....but an option...let's see, about 20 minutes? About a mile , I think...My DH did it in under 10 one day when he forgot his ticket...but he is 6'4" and can move when he wants to! There is a paved walk all along the Crescent lake that leads to the entrance of MGM, you just follow alon that walkway. It is nice at the end of the day if you do not care to wait for a boat or ithe boat line is relally crowded. We tend to walk vs. standing...either way we are on our feet!
Epcot walk seems shorter to me, less than a mile for sure. The path takes you to the International Gateway entrance, by France/England. So pretty. I like to walk as you can see the resort grounds, animals, just more peaceful to us. We use the Friendship boats a ton also, but do like to walk. The boats make up tp 3 stops, so it can be around the same timing to walk vs boating, just a matter of preference and tired feet! You can also mix it up...get off at different spots and walk back if you choose from say, Y/C to the S/D and enjoy the Boardwalk.
I think it is worth it ot give the S/D properties a chance, but they have gotten up there is price like everything else, but again, we have always had a great stay there.
Pam