Over on InsightCentral, Scott goes by KLR3CYL and has a website, killer3cylinder.com. He sells (among other things) Daewoo Matiz springs which fit the Insight's rear axle and have a higher spring rate. I had him cut approximately 1/3 of a coil before shipping so ride height would be almost exactly the same as stock, despite stiffer springs.
Contact - Killer3cylinder
Rear springs - Insight Central: Honda Insight Forum
He also has premade hitches which fit the Insight, replacement aluminum underbody panels, and a turbo kit.