Do window blinds pointed (twisted) up let in more light or do blinds pointed down let in more light. My wife and I can't seem to agree on this.

depends on the angle of the sun.

if the slat in the blind is directly in line with the angle of the sun (from above), it allows the maximum amount of light, while still maintaining a degree of privacy from people looking into the windows (from below).

conversely, turning the slats perpendicular to the angle of the sun gives maximum shadowing, while still allowing vision in the other direction.

as far as turning the blnds completely closed, whichever direction the gaps close the tightest should theoretically block the most light.

Rotating the slats so that you can see down when you look out the window blocks the direct sunlight from entering a window near ground level.