The problem with making forts better or more usefull at present is that the AI dosn't really utilise them, so they are too easily abusable in 'gamey' ways as mentioned. You get to do this but the AI dosn't, so it's a clear player advantage

Not that I'm complaing about the AI on this, the relatively simple ( to a human) forts tactics described in this thread would be very difficult to encode for an AI, and indeed, you don't see them doing it.

I'm reminded of the classic Civ style game Alpha Centauri. It was amazing and had all these well designed and balanced features and improvements over CivII. The problem was that the y forgot to tell the AI about most of them so even on the highest level the game was a breeze (though still very enjoyable).