"But if people are willing to pay $20 for a 3GH stickminer with fixed voltage, would people still pay $25 for an 8GH stickminer that can be adjusted to 15GH and still come in at more power-efficient than any miner you can actually buy anytime in at least the next month?"

I say HELL YES!!

A fixed V 3GH stickminer @ $20 = $6.67/GH/s
An variable V 8GH/s stickminer @ $25 = $3.13/GH/s
A tweaked variable V stickminer tweaked to 15GH/s @ $25 = $1.67/GH/s

Remembering that a stickminer is not a commercial product (one is not going to build a 1-2 PH/s mining farm with them) that is, IMHO, a very competitive price.

I'll send ya' .2173 BTC for 2 right now if that's you're price point.
Ship'em whenever you get them built.