Just to follow up on @CptLucky8’s suggestion, I redid a series of pictures related to those posted above and am presenting them in order of increasing 3D effect. CptLucky8 is right in that one gets more 3D bang for the buck with Contact Shadows as opposed to Ambient Occlusion but I think AO provides useful 3D clues as to overall volumetric shape whereas a contact shadow is more of an underscore next to an object alerting one to its 3D presence. I tried ULTRA settings for both individually or combined vs. no settings at all (OFF) for either and in order of increasing 3D it is:
AO and CS, both OFF
AO ULTRA, CS OFF
AO OFF, CS ULTRA
AO and CS, both ULTRA
AO = Ambient Occlusion
CS = Contact Shadows
To me ULTRA Contact Shadows or the ULTRA combination of Ambient Occlusion and Contact Shadows is a little bit like going out on a date with a woman who’s applied too much mascara and eye liner! 
If you click through the opened pictures with your arrow keys, when you get to the ULTRA, ULTRA picture, you can jump back and forth between ULTRA, ULTRA and OFF, OFF by alternating between the left and right arrow keys.
Settings as previously described except:
Ambient Occlusion OFF, Contact Shadows OFF
(click to enlarge, arrow key to cycle views)
Ambient Occlusion ULTRA, Contact Shadows OFF
(click to enlarge, arrow key to cycle views)
Ambient Occlusion OFF, Contact Shadows ULTRA
(click to enlarge, arrow key to cycle views)
Ambient Occlusion ULTRA, Contact Shadows ULTRA
(click to enlarge, arrow key to cycle views)
