And Slightly better audio tools. But this can be done outside iMovie and so much better.
• Download Audacity (free audio editor)
• In iMovie Export out as QuickTime Expert mode and as audio only in .aiff format
• Import into Audacity and adjust to Your hearts joy - Save as .aiff
• Import back into iMovie.
Done
• Color correction - not better
• Picture qual - brightness/contrast - as in iM HD (5)
Sorry