thenightgaunt
Explorer
To add the the discussion: in the novels and written lore about Waterdeep, aye, there would be no defense against an experienced well armed, well equipped Spelljamming vessel. At this point, many of us are long past relying on this lore. My Waterdeep, while using the available lore, has evolved to become is a much different City of Splendours. In my Waterdeep there is the Hazrid Tower - near the City of the Dead, which with it's 20 elegant piers reaching like a spidery tree into the skies, is actually a series of berths for Spelljamming vessels. A DnD Spaceport! While Spelljamming is not the stuff of the common man, and indeed for many remains the stuff of mystery - virtually all common folk do not realize these vessels are anything more than airships.
Exactly my point. If you're gonna run Spelljammer, you can't run off of the rules as they are in the books. You've got to be the kind of GM who can adapt and change rules and setting info to make it work. You need to be able to smack down any bitching ruleslawyering players and say, "this is how I'm running it".
I like the spaceport idea for waterdeep there. Though I'd be resistant in bringing it in. Spelljammer was one of those settings were magical items were abundant to the point of absurdity. Just look at The Dock on Faerun. A city run by Arcane where any magical item can be bought. Of course, a good GM can fix all that and balance it with the earlier system.
In my old SJ game the players made their fortune selling waterdeep it's first spelljammer helms and giving it the power to defend itself.