Was it Paul's point that those Greeks were living off borrowed capital?
I think we can draw that point from the narrative as a whole, but I cannot see how the apostle would have been explicitly making such a point. This passage is often referred to as the model apologetic in finding common ground with unbelievers; but if read carefully we will see that the apostle was in fact diminishing what they thought they knew, and offers negative critique of this idea of an unknown God. They were still reflecting the times of ignorance when God left men to "feel" their way to Him. Their feelings led them to worship all kinds of things in His place, and God let them go on in their folly. But now there is a full revelation of God and His will in Christ and He commands all men everywhere to repent. Far from pointing to common ground the apostle demonstrates that there is nothing common between Christ and idols, and God's exaltation of Christ demands a whole new way of thinking and living.