You can set a shortcut key for Audio gain. Then either highlight all the clips, or close the bin and click on the folder icon for the bin, hit your shortcut and adjust the gain. It'll effect all the clips at once.
Okay, great. This is non-destructive, right? I don't want to write any changes to my original media on the drive.
Yup, it's non destructive.
Nifty little trick.
You learn something every day.