I too have looked many times for this. I use this all the time in Pro Tools cmd+option+[ and ] zoom waveform and cmd+shift[ and ] zoom MIDI events and then on the Icon you can do the same with the wheel and it is very smooth (no MIDI zoom though). What I love is you can actually also go smaller and cmd+option+ctrl+[ returns you to your default value. Cubendo only goes larger which for the most part is more often what I need.
This Sound on Sound article lead me to think there was a shortcut.
“I’ve set these as Option-G and Option-H on my Mac, so that the ‘G’ and ‘H’ keys control both horizontal zoom (without the Option key) and vertical zoom (with the Option key). Of course, you could similarly use shortcuts to increase or reduce the height of the waveform within an event.”