The historical data already take into account the rough current distribution of such voters, and the efforts of national political organizations that try to put money into competitive races. If arguments like mine become more widespread in the future, they will change matters.

This post explicitly limits itself to causal decision theory to help avoid these issues, but I'll discuss them in a future post on decision theory complications. The second parenthetical was an acknowledgment that there is more to say on it.

Experiments and studies like the ones you suggest do seem like they would be helpful in navigating those complications.