We haven't stayed offsite for XMAS yet, but we will be doing so this Dec. 19 - Jan 1. We'll be close to you in a 6 bedroom house at Oak Island Cove, which is just behind Splendid China, which you'll pass on your way to Windsor Palms. We stayed at Windsor Palms last year for Thanksgiving, and I've been on numerous other Disney trips, and have also probably read some of the comments you've seen about being off-site at XMAS, so I feel I'm qualified to comment.
I think as long as you plan to get to the parks early (like 30 minutes prior to opening time), and you stay there all day, you should be fine. This is our plan, and I feel that the benefits of staying in a house off-site far outweigh on-site for us. We'll have 3 kids ages 5, 8, 8, an 80 year old grandmother, and a couple of 50 somethings as well as several 30 somethings in our group for a total of 12. I'd recommend taking your $3000 in savings and planning a nice, leisurely sit-down lunch each day as a mid-day break. The convenience of being able to eat breakfast as your house, as well as doing a bit of laundry there will be great. It will also be nice to all be together, but with separate sleeping areas. I say stick with the house.
Also, be sure to plan to go to a park that's not the early entry park of the day, and probably avoid Magic Kingdom on XMAS. For New Years Eve, I think our plan will be to go to Animal Kingdom because it will just be us with our 2 kids at that point who wouldn't be able to stay up for midnite fireworks anyway. I've read that the Animal Kingdom is least crowded New Years Eve because it closes earlier and won't have fireworks, but that's fine for us.
