Tactics for the Swamp (Fortress).

Well, here, as with Might and Magic, there's one small detail. It doesn't work against Necropolis. So, I'm thinking that when playing against Necropolis, Gorgons can be upgraded last, and the 7,000 gold, as well as 10 stone and 5 wood, can be spent on something else. Is the +1 speed increase worth sacrificing something else for? We need to think about Wyverns. There's a whole +4 speed increase, which is significant and critical. And in general, if we're talking about a fast and powerful army, upgrading Wyverns is what the doctor ordered.
By the way, I hadn't noticed: does the Expert Water Magic spell weaken only one enemy snake at a time, or all of them? Or does that property only occur on magical terrain?
P.S.: Azure Dragons aren't for me. I'm more drawn to Stronghold. =)