this is similar to the Maxon Power Booster (which you can make just by changing the 2 caps to 470n caps. my friend Dan was asking about it so I thought I would make one cause I love treble boosters.
This looks cool! That 1590A plug-in build is super cool too! Neat idea.
Your electret microphone preamp looks interesting too. I got a couple of those from Tayda to make a little mic for my iPhone, but haven't used them yet