I think those play a smaller role, for the following reason: If modern art was primarily about the social aspects, you'd expect most modern art to be stuff like a perfectly blank canvas or a urinal, because those are direct signals of the "coolness" of the artist (who else but a charismatic person can sell a blank canvas?)

If art was more about tax evasion, etc, then modern art would probably be more photorealistic or otherwise difficult to create (since this would make it easier for outsiders to assess the scarcity of an asset)

But I agree that the modern art market is multifactorial in nature and that there are elements of both involved.