Is it that they couldn't offer you rooms at another Disney resort room only for the first and last day, or is it the pricing didn't work?
We did off site the first and last day one year, and it worked nice because it was a change of environment, cheaper and less crowded at the pool.
BUT we also had our car to do so.
You could stay off site and go to another park for the day. Those parks have nice hotels near them too.
I'm not trying to take away from the Disney experience, but trying to paint an Orlando experience picture to maybe help with the disappointment.
What time are your flights? If they don't give you a full day at the resorts anyway, it might be worth staying at the Hyatt right at the airport. Then you don't have to rent a car and can still use Magic Express to get back and forth from the resort to the airport.
I think a lot of people book and end up canceling for one reason or another. A lot of times flights definitely make a different. But yes it is harder to adjust your Resort stay based on the flights you end up with. There are ways to make it fun. I try to at least. Life is too short and best plans can be messed up if the adventure isn't embraced.
Hope it ends up being the best vacation ever.