Firefly: Awesome tips; I had noticed something was causing what you had mentioned with edges, but I wasn't quite sure. I'll be sure to eliminate that contrast
As for the sparkliness, very intentional, I played around with it for a while until I thought I'd hit the mark. And for the reflection, that's a superb idea! I'll definitely play around with that idea later today, and hopefully the greens I have now will work to make that happen so I don't need too many (if any) new shades. (on a side note, the phrase "dither monster from hell" made me laugh harder than I should've; I'm considering making that the unofficial title of the piece
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As for the more technical nitpicks, I'll hold onto those for later when I can look at them in detail and make the adjustments. And of course thanks in advanced for the graphical nitpicks 
Considering the fact you haven't shown distress that I'm using so much dithering, should I take it that I'm going in the right direction in terms of dither? 
Well, I'm far from all knowing

If something doesn't scream 'wrong' to me, it seems okay to me to explore that direction. The dithering is a style choice, one that you are carrying off fairly well. Actually, I just realized the most prominent area of dithering is wrong shape-wise, and that's what most struck me as 'off'. See, you shaded that surface like it was convex, but it's actually a concave surface under a convex one, so complicated happened

hard to explain w/o an edit.. you have the lighting hitting the surface (which is transparent, so only a sheen) and the light bouncing off underneath.. surfaces at different angles.
EDIT:

Not quite up to the standard of previous edits. pixeling with a touchpad is insanity inducing... Anyhow this is my suggestion for that band of eyeris, some of the overly-contrasting firefly bits, and the eye edge AA, which turned out harder than I thought. Personally I'd opt to modify the shape slightly so it AAs better.. that's definitely a style choice though.
On the subject of larger dither patterns.. one reason I can see in this pic to avoid them is that they create bogus edges at this resolution / display size. particularly when you look at whole or partial diamond-formation that's bigger than
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It shows up as a discrete shape. I guess what I mean is that the scale of dither patterns that work -- if you are going with traditional pattern dither -- is strongly dependent on the display scale of the object being rendered. Sky gradient, on a pic of this scale? 4x4 patterns will probably be effective. Smaller, more tightly shaped gradient? 2x2.
An example of where 4x4 is appropriately used is
Przystan by Lazur
Also on the subject of dithering, have you intentionally mixed the alignments of the dithering patterns? IMO this gives Twilight a little stubble

when you look at the darkest shade on her jaw. I am a fan of the directional crosshatching look you have going on there... it doesn't require a switch of alignment to achieve it though IME.