Since hitting more than 1 shield bubble at the same time is often the way that shield bases go down, I'd argue that AOE is incredibly important when lobbing artillery.
Any hit on 2 shields will do full damage to BOTH of them, and this can only be done reliably with AOE. The more AOE, the easier it is.
I've noticed that intentionally 'target ground'-ing in an attempt to hit more than 1 shield seems much more effective than just targetting a single shield in an attempt to overwhelm.
(Somewhat related: Although the micro is borderline impractical in all but the most stagnant games; you can use as few as 2 mobile missile launchers to destroy 2 shields with some clever target-ground micro, as long as you ensure that you hit both bubbles at the same time, to ensure they all go down together. This is easier done by targeting the edge of the shield bubbles, at a point where they intersect. It's even possible against 3 shields, but a player would have to be SO much better than me (I'm rubbish) to do that in a real game, since hitting all 3 requires more than just ground-targetting the intersecting edge (you have to fire into the very centre of the 3 where they intersect). 2 shields, though, is relatively straightforward if you have the time to micro.)