I apologize if I missed this discussed elsewhere, I skimmed over the forum and didn't see this particular question discussed.

I have a set of black plastic handguards and a black plastic stock which I want to coat in a flat dark earth. Off the shelf I have Aervoe Field Drab, Brownell's Alumahyde II in Magpul FDE, and a variety of Krylon and Rustoleum plastic-specific paints (albeit mostly satin) as well as their respective 'Camouflage' lines.

My goal is to have furniture which is durable to regular handling, however it does not need to be impervious to solvents as I'm fine with moderate wear as I use it. I plan to de-grease and wash the parts before coating. All things being equal, and preferably using my existing solutions, what would you recommend for the furniture?

I used Krylon , easy to touch up.

Totally up to you.  It's sorta a sliding scale between durability and cost.  A good middle ground that I have found is Dura coat.  It coats furniture well and is pretty durable.  On the low side, any good flat rattle can paint will do.  But it will will wear off.  On the high side you would have non-baking Gun Kote and Cerro Kote, which would be much more durable, but also much more pricey, including application equipment.  

I've had good luck with Alumahyde, but use Duracoat almost exclusively now.  Like I said, it's just a good compromise between ease of application, cost, and durability.  I like their Magpul FDE and Medium Coyote Tan.

I'd go with the Alumahyde since you've already got it. It's fairly durable (more so than regular spray paint), and easy to apply. It goes bad after sitting for too long though, and will start spraying gobs if the paint gets old.

Standard FDE Cerakote is best.  Duracoat has a good taupe color.  Air cures. Easier to learn.  Takes 3 weeks to fully harden