I am pretty sure the new Disney museum is opening up in October, but I am not sure when exactly. It is going to be over in the Presidio, by the GG Bridge.
I am not sure what you did last time- there is the obvious Pier 39, Fisherman's Wharf, great shopping at Union square and the mall, you could do a walk across the bridge (if the weather is nice), Ghiradelli square, plenty of good shows to see. The California Academy of Sciences just re-opened which I haven't been to it yet since the re-opening, but it is like an aquarium/natural history museum and they have a new rainforest exhibit that is supposed to be really nice.
Golden Gate Park is a great option. You can get a picnic lunch and explore. The little Shakespeare Garden is a cute spot to sit and eat. You could go to the Conservatory of Flowers- It is a beautiful place to see even if you don't go inside. The outdoor Arboreteum is a great place to walk around and it's free. You can check out the windmill. The Japanese Tea Garden is pretty, you can walk around and see the gardens and even have lunch there (I have never actually eaten there, so I don't know if it's good, it's always crowded). And China town is a neat place to get some amazing Chinese food and unique souvenirs.
If you go across the bridge into Sausalito (it's a little town with amazing views of the bay, cute shops and good food), you can have an amazing dinner at The Spinnaker, right on the bay! Tiburon is another beautiful nearby town (across the bridge in Marin) with cute little shops and good eats. But Sausalito is just right across the bridge.
If you want an amazing (expensive) ladies brunch, you can go to the Cliff House. If you are looking for cheap eats, Sears Fine Foods over by Union Square is yummy for breakfast and lunch.
If you luck out with a really nice day, you can go down to Ocean beach or something too. Sorry I don't know where the new Marriot is, so I don't know what you are close to.
Have a great time- hopefully something on here helped