High performance from lightweight Hondas
You say there are much better platforms than the econobox Civic. Actually, since '85, the Civic platform has been sold with a high-performance engine version in Japan and in Europe. We didn't get these versions in the U.S. People here in the states are simply putting these engines or equivalent hp into the Civics and CRXes here, and making the suspension mods as well. These cars are just as suitable to modify as they are suitable right from the factory in the high-performance Si-R versions Honda has sold for over a decade in Japan.
The '90-'91 Japanese market CRX Si-R was rated by Honda for 0-60 in 6.7 seconds and 1/4 mile in 14.5 seconds, with a factory limited slip differential available. These chassis, shared with the Civic Si-R, were made for this kind of performance right from the factory.
As for better platforms, that depends on ones definition of better. My definition, from a sporting perspective, is that lighter is better. Thus I, and many other CRX and '86-'95 Civic enthusiasts, have no particular interest in a 2,700 lb. RX-7 or a 3,100 lb. Corvette or Supra. The nimble, go-cart feel of a lightweight Civic(not all Civics are lightweight)/CRX or Insight is more entertaining of a platform for me and many others, than those much heavier cars.
Getting alot more hp out of an Insight surely would be entertaining, just as it is getting 170 hp out of my B16A-powered (engine from '91 CRX Si-R)'84 CRX, which I've owned since new, with the original 60hp 1.3 liter engine earlier.
There may be cheaper platforms out there to modify, but Honda quality is worth paying extra for.