Good post. Several reactions:
On the film "Arrival", if the gift is seeing into the future then you don't need to worry about intent - you would know which first contacts would be benign.
I don't think it is a given that there is a general resource constraint in the universe.
A reason we might have difficulty detecting civilizations is also cryptography - I would guess most transmissions would be made to be effectively indistinguishable from random background noise.