If I had access to a Villa on I-Drive, I certainly would not be staying at a Disney hotel.

That's not to say that Disney hotels aren't great (I've heard nothing but good things) and staying on Disney property does have some advantages, I don't think its worth it to go out of your way to stay there if you've got another place lined up, especially since you'll have a car. Plus, if you want to visit the other places in Orlando, like Universal, then you'd be leaving Disney anyway.

Of course there's plenty to see and do in those other cities, although, I don't know where they would fit into your schedule - especially Seattle which is a long way from any of your other destinations.