It would be nice if (as you're adjusting the velocity of a note in Piano Roll,) the new velocity were updated accordingly in the velocity map (bottom part of the Piano Roll view.) So, if a note is at 64 Velocity, and you click the up arrow, as the note velocity goes to 65, the velocity map display of that note grows to 65 as well. If you then hold down the UP arrow, and the note goes to 66, 67, etc...127... the size of the velocity map on the bottom grows AS WELL!
 
Added feature request: As you're editing a single note velocity, the other note velocities (if shown) would DIM a bit, to highlight the note being edited.