I am trying to understand  how onslaught of scouts would help.

Are you saying that players leave their town unshielded because they know they cannot be succesfully spied on?So any pot luck attack is risky and  you want to eliminate the risk?

You wouldnt be able to attack or scout  anyway if they were shielded.So there is no difference here?

Are you wanting to test for traps ?Isnt any unshielded large influenence city likely to be one?

Are you wanting to scout, then decide if you want to attack, or just kill lots of scouts for the points?

Are you wanting to see what is in the town, in case the next time it drops shields you can attack?

The game is what it is, and the clever people come up with schemes to take advantage, sometimes the programmers move to remove them, so you could be lucky.