Typically, in September you will have less families because the kids will be back in school. You will probably find more mature couples, girlfriends on the town and a sprinkling of gay folk. Many of the Baltimore cruises draw people from this immediate area, DC, WV, possibly PA, etc.
The other thing to consider is that while Grandeur is still in pretty decent shape, she is 10 years old and is not as nice as some of her newer sisters that go to other destinations. The alternatives for Bermuda in September would be:
Explorer out of Cape Liberty, NJ which is 3 hours away. Explorer is newer and is a Voyager class ship. It also has an onboard sea lab associated with the Univ of Miami
Empress of the Seas out of Philly: This ship docks in Hamilton and St. Georges. Empress is smaller than Grandeur but has recently been spruced up. The cabins are very small. Empress is a bit of a misfit in the fleet but many folks like her.
Celebrity Zenith. This ship is also older but docks in Hamilton and St. Georges. It is pricier than RCI but it does not offer cabins with balconies.
Norwegian Crown also docks in the cities but she is a bit older and smaller too. Norwegian has the freestyle dining but she is not as nice as Grandeur or Explorer.
On Grandeur, you will be docking at the Naval Shipyards, you can either take the excursions to the towns or take a ferry. They are easy, reliable and inexpensive. http://www.seaexpress.bm
I also don't mean to plant any fears but keep in mind that September is still hurricane season. Your itinerary could change (extra day at sea for example or worst case you could be shipped up to Canada, which happened to the Voyager last year. People were pissed about that change.)
I think overall you will be happy on Grandeur, especially since the Locust Point terminal is so convenient off i-95. Keep in mind though, Baltimore is a secondary point of departure and Grandeur is due for a refurbishment soon. Just keep your expectations in check. I would not worry about any intolerance. Harry's article covers all of that pretty well.