Most useful things

• Review the hardware designs, schematic and layout, for errors or possible improvements.
• Review the overall system design
• Contribute mathematical analysis of system aspects, along the lines of the "Resolution" post
• Contribute fleshed-out ideas
• Review the Issues section

Useful

• Mention the work to people who might be interested, or even better, might be able to contribute.
• Keep an eye out for anyone else doing the same thing, so their good ideas can be incorporated.

Ehhh

• Consider donating to Kicad, this would've been excruciating-to-impossible without good free PCB design software.
• If you know of any open source circuit simulation software, donate to them, too. I got by with Micro-Cap, now that they're giving it away, but, ugh. Kind of rough.