(stuff)
Balance would definitely be an issue here as there'd be some way to make some powerful combination to produce an Everything Proof Shield. Not sure how to avoid that other than GM'ing.
(more stuff)
Resources:
To have resources such as trees, gold, magic crystals and other such stuff be gameplay changing is sort of unnecessary. It's usually in the description of the city that it becomes known that what the city runs on and what kind of characteristics are there. It'd give alot more reason to have a 2nd/3rd age landshift though.
Events:
Seeming as the game is quite army centric, and catastrophes are a way to keep others down. Event's are, as I see as, a not so destructive catastrophe. I'd describe Donnie's rise of Avalon more of an event as opposed to a catastrophe. It just depends on the writing I suppose.
Yeah, one time I had an interesting idea for a Combined Arms advance that gave -1 under normal circumstances, but +1 for each "type" of army (infantry, armor/cavalry, air, navy, artillery) in the stack. But it would be hard to stop stuff from becoming OP, especially in combination. Even in the above example, the GM would have to make some calls on what constitutes a "type", to prevent me from stacking ridiculously large bonuses. Even though the specific functionality in this case just encourages people to nuke the incoming stack if it gets too large.
For example, let's say we have a civilization called the Yuri Dominion. First, the Yuri Dominion takes a Cloning Vats advancement that gives them two armies for each Raise Army action instead of one. Alright, a little powerful, but might not seem so bad, especially when there are other ways to get armies on the cheap.
Then they take the Grinder Universal Recycler advancement, which allows them to disband an army or city to recover the points it would cost to make it. By itself that's not too bad, it just gives them a little flexibility by letting them "undo" certain moves.
But wait, Cloning Vats gives him two armies for the price of one! If he dumps his points into armies, then disbands them all with the Grinder, he'll have twice as many points as he started with! An infinite point loop like this would clearly be OP, and the GM would have to make some sort of call to prevent it. In this case they'd probably have to use their GM power to say that armies only recover half their cost (rounded down), or that the free army granted by Cloning Vats does not give points when recycled.
Resources would be cool but difficult to implement, since we'd have to build a whole new ruleset around those. Though I suppose players could be allowed to make up resources and their benefits as they go with GM approval, similar to Advances, but we'd have to establish some limiting factors to keep Resources from becoming a 3-point or 1-point (avatar action) Advance.
Also, Donnie's warship was a Catastrophe because he nuked Trask with it.