Should this be the time for the Diplo Leader to post a poll on how we should handle the Zulus? From there, I'd think it would lead to the Military Leader as I would guess that most of Fanatica would just assume remove the Zulu "threat" sooner rather than later. We all know that the Zulus will find a way to sneak attack at some point.
Don't know how the funds are, but I'd probably lean toward a diplo buy. From there, I would actually prefer to settler-starve the city and build further away from Spycatcher (after relocating units in Spycatcher of course). I STILL think that there's a good chance to find another special off-shore. If we have to take them by military, I don't think that they'd be so advanced as to have feudalism, so even a single crusader can likely take the city over a few turns. Even if they did, I'd still attack with crusaders!!
This is a great time militarily speaking, and I think that we should really press the advantage. Mounted units like (hopefully some verteran) crusaders (and BOY if we could get dragoons) are just great to take out almost all pre-gunpowder units - including pikemen. Unless a vet pikemen is fortified behind city walls, they'll win a huge percentage of the battles - and can even take out those pikes fairly often.
I would make contact with the Zulus first and play nice to get their map!! This will likely show us what is off-shore without having to send a trireme and will also let us know where the Zulus have set up. Gift them a useless tech or two and they'll be only too happy to swap maps. Then stab 'em!
So let's get these polls up and start the process!!!