The closest thing to a performance mod discussed here has been exhaust and air filter mods. There are very long threads on both of these so if you search for air filter/exhaust you'll run across them. I think you'll find they were able to get additional power but took an FE hit. I've tried lightweight wheels - not for performance, but for FE. However they didn't increase either.

You may be interested in the Camary hybrid discussions. The Camary seems to address a lot of the power issues folks have without sacrificing too much FE. One HCH II owner traded his in for the Camary recently and has a nice comparison writeup.

*** Retired after 65,000 outstanding miles ***