Last night, I won a game (v1.1, Resoln / Ceresa, large map, 8 players, challenging AI) in around 330 turns using the Spell of Making victory condition (my first such win). I thought it was a bit too easy. My first reaction was: the Spell of Making tech is too early and it should be an end of game tech. After thinking about it for a while though I actually agreed that it is probably better it's not the very last tech as it gives another different way of victory for the players that want to pursue it. However as it stands, the spell of making victory condition a bit too easy because of the following:
The AI players don't realize you're about to win the game. Every time you build one of the towers required for the spell of making, your opponents should get a notification (I don't know if they do) and you should get bad and progressively worse diplomatic penalties from every opponent you already met. By the time you complete all 4 towers, it should pretty much be instant war declaration from everyone you met with no possibility of making peace. Also, I didn't check if this is in the game or not but any time you lose one of the towers required for the spell of making, the spell of making you are casting should be interrupted so one way to stop a player from casting the spell should be capturing/razing a tower city she owns.
Now even with all this, stopping spell of making may still not be possible. You can rush build the towers very easily in a few turns if you have a lot money and 10 turns is a very short amount of time to cast the spell. No one may be able to stop you in time even they are vastly more powerful than you. So, I also think a combination of increasing costs of towers, casting cost and time of spell of making may be necessary.
In my game last night, before I started casting the spell of making I was at war with Magnar and Yithril. After I started casting the spell of making, I actually paid them off to make peace (95 gold and 114 gold or something) even though they hated me. That shouldn't be possible at all when I am less than 10 turns of winning the game.
What do you all think?