I think what really sets Art Deco apart, and what makes it closer to what came before than what came after, are the decorative embellishments. These are what make the buildings engaging at the street level.
Can an architect here comment on the cost of such embellishments, such as terra cotta molding or mosaic friezes? Is it prohibitive, is it simply a "nice to have" that's never had for property developers, or is there a stylistic bias against embellishment?