To quote my daughter, "totally do a BIP, it's way better"
I unfortunately have no experience with taxi's in the San Diego area as when we go, I either rent a car, use the trolley or bum my daughter's car. I would think the Sheraton can recommend a reputable cab company.
I have not been to the Maritime Museum so again, I cannot advise on that one (it's on my to-do list). There's also the San Diego Air & Space Museum if you want another aviation oriented opportunity.
Segway tours are a great way to see a city and cover lots in ground in a short period of time. We did one in Anchorage this summer and it was a kick! I'd certainly give it a whirl if you're so inclined.
Enjoy your visit ...