St. Thomas was one of the most accessible ports I've been to. San Juan is OK too, except the cobble stone streets. It's a bumpy ride.
I just think the E. Caribbean is much more friendly ports for scooters & chairs. I'm leaving this weekend for E. Caribbean cruise (11 night) and can tell you more when I get home. Email me at firstname.lastname@example.org . I will be home by the 14th of April and then I will remember to tell you more information.