Keyboard shortcut for increasing/decreasing veloicty?

Have you considered writing two CAL scripts, one for velocity up, one for velocity down and binding them to keystrokes? 

Using a standard text editor, create the Cals using the information below, save them to your CAL folder (See preferences | FILE | Folder locations to see where CALS are stored) and then bind them to the keystrokes of your choice.

Note, these cals simply increment and decrement the selected note's velocities. A relative increasing and decreasing would require different code.

The cal script for Velocity up is as follows:

(forEachEvent
    (if (&& (== Event.Kind NOTE) (< Note.Vel 127))   
        (do
            (+= Note.Vel 1)
        )
    )
)
 
The cal script for Velocity down is as follows:
 
(forEachEvent
    (if (&& (== Event.Kind NOTE) (>= Note.Vel 1))   
        (do
            (-= Note.Vel 1)
        )
    )
)