I think frosting the cut out area of the tint will definitely help it pop - lit and unlit. As an alternative to engraving, I've used a sandblaster to frost glass with pretty good results & imagine it'd work good on plex as well.
Mask the area with several layers of masking tape, cut out the area to be frosted with an exacto knife, blast with a cheap hand held and playsand. Can't dwell on the edges too long cause it will eventually eat through the tape, but a few light passes are all that's needed to get a nice uniform frosted effect with sharp edges. The engraving looks great, but blasting's bound to be a lot less tedious.