Finally got the Plexi over the monitor:


Cut to the perfect size by TAP Plastics
http://www.tapplastics.com/. Literally pulled it out the shipping container, peeled off the protective paper, and popped it into place.
It's their Solar Grey Acrylic. It's a LITTLE darker than I'd like, but even without masking the back it's hard to see through it to the mounting brackets. And as you can see, the AimTrack bar shines through just fine.
I still might find some small quarter-round trim to frame it a little more, but as is I think it looks alright.