Is this the ship that alternates the pier with the Grandeur of the Sea?
If it is, you should have an easier time getting off the ship here than if the ship docked in Hamilton (where you got off on deck 2 and went down a ramp). The ferries that take you to Hamilton or St. George say they accomodate wheelchairs. There is an area at the end of the ferry that looks to be secure for wheelchairs--please double check this with the people that operate the pier since I'm not wheelchair dependent.
In terms of things to see and do it is somewhat personal preference. I enjoy watching the glassblowing and snorkel beach I think would be accessible. There is also a small mall in the dockyard area if that interests you.