10 days is NOT too long for UO. We like the laid back feeling of no dining reservations we have to get to, or no Fast Pass Pluses we have to run across a park to make. We love the fact that at UO we can spend more than 1 day by the pool with adult beverages wondering where we might eat that night, or getting up later, because we don't have a Fast Pass we have to get to.
We love WDW, in fact my daughter works for WDW and she will be bringing us to EPCOT for a day while we are there, but this year we rather have the relaxing overall feel of UO. Plus next year we plan on doing something from our bucket list which is a visit to
Disneyland. So we'll be getting our Disney fix then.