I’m all for staying on-site. Any of the All Stars. There are so many advantages, cost being one. You just take a Disney bus to the exact park you want that day. You have no parking fees, gas, etc. plus you save a lot of time getting there. They used to also have "special hours" where the park was open early/closed late for Disney on-site hotels. It was less crowded then and we got "more time for our money". You are also "part" of WDW all the time. Cost/benefit: I would never do it any other way.
As to the time of year, I’m not sure but have you considered taking your daughter out of school for a few extra days to make a longer week (like around MLK day or Election Day or any of those other holidays?) Not that it’s for me to say, but I sometimes have my daughter miss a few days of school when we travel. I think its worth it and the school has never given me a problem (I just say we have to go "out of town" and that she will miss a few days).