There is no direct bus from the all-star resorts to the boardwalk. But, you can go to the nearest park and catch a bus from there to the boardwalk. One year I think that we actually rode a boat there from MGM. Maybe someone can confirm that for me.
you ride the bus to Studios (disney not MGM these days).
then you walk to BW or take the boat.
now this only works as long as Studios is open. Once it is closed then you need to take the BW bus (which can be hard to find - so ask) to either the park that is during EMH that night or DD.
go to mgm and walk over to boardwalk..its well worth the bus drive and walk..you can walk into epcot and miss all the crowds,,its great,,just sit and relax and enjoy....i just did it 2 weeks ago 3 times,,
If you're at EPCOT you can leave via the International Gateway (located in the World Showcase between the UK section and France) and walk over to the Boardwalk.
As stated, if you're at the Studios you can take the boat or walk over to the Boardwalk (about a 15 to 20 minute walk at a normal pace).
To get back to ASMu, you will need to go back to one of the parks or DTD and catch a bus back to ASMu, OR you can always catch a cab right outside the resort .
It's definitely worth the trip over there, though.