Thanks all! It's certainly been a busy few weeks painting this helmet up. Still more work to do, but the brunt of it is behind me. 
mrgr8ness,
When I do the fine scratches, I go down to the gelcoat layer and just leave 'em like that. No silver added.
And yes, the gray on the dome/lower cheeks is a slightly darker shade than on the mandible areas. You're exactly right that I darken my SP Lark Dk Gray with a few drops of PRR Brunswick Green until the contrast against the PO Green is more evident.
I have had good results with both enamels (Floquil) and acrylics (Polly Scale) on my helmets. With the exception of the Boxcar Red. . . the enamel just looks so much better (to me.)
The Floquil paints are very 'pigment heavy.' So if they sit on your bench for a while, they can settle quite a bit. I always give my paints a good stir before using them. Not just shaking them, stirring them.