If you're on MC 7.0 at least you can now have access to a shortcut to add or remove gain.
You have to turn on the feature first and then you'll see a little icon in the lower left corner of the audio clip. Clicking on it will reveal a slider so you can lower/raise the volume.
But don't get too excited! If you work with dual mono tracks (L-R) you'll have to set the gain for each track...
So not as quick as FCP but faster than before.
I also just came across a post saying that there was a keyboard shortcut that I haven't tested yet. But it seems it applies the effect to the whole track
ALT(OPT) + SHIFT + Arrow UP/DOWN adjusts Clip Gain in Timeline
(when Clip Gain is visible in timeline settings & Track selected)