Just a point, but this is a pet peeve of mine (and probably irrelevant); I'm sure psugar would agree:
SD is known for its deep gameplay that builds to a crescendo as the game progresses
A crescendo is not a climax; one doesn't build towards it in the way you mean. The crescendo is itself that build-up. The crescendo
is the movement towards the climax.
Terribly sorry to bother with such irrelevancies... but I can't read them without prejudices...
To be entirely honest, I don't think that, regardless of whether or not the siege fleet can be stopped, the strategy is really viable. In mediaeval times, would you have tried to swamp you're opponents with trebuchets? In the American Civil War, would you have tried to swamp the other side with only cannons? Today, would you attack the enemy's home base with a whole lot of artillery, or even howitzers, and nothing else?
If you answered yes, then you belong in run-of-the-mill RTS's.
If you answered no, think about why. I can think of a couple:
1) Your units would be useless against things like cavalry/light tanks etc.
2) Regarding the expense of siege units (a trebuchet is extremely difficult to make, apparently; artillery and cannon are expensive), you wouldn't do a charge with them, even to take out the enemy home base.
3) You can't really take anything on except structures (here, planets) and tight troop concentrations, though if one is going for the home base then this doesn't really go to the detriment of the force.
The AI ignores all three of these points (though from the sound of it it doesn't really care about the third). Is it then behaving rationally? No. Why not? Probably because the statistics of these weapons are not in the character of siege units, and don't stop the AI from using them rationally.
In my opinion, that's good enough reason for a nerf BUT i think Schod's right in that we should wait at least a week to see whether these three reasons are actually enough to come up with a solution to the problem that doesn't require an arcane formula. THEN we should complain.
Sorry about the length