Here is an update about this topic with some (hidden) functionality:
To set all the selected Notes to the same value:
- Select the notes in the Piano Roll
- Open the MIDI Draw Area so you can see what is going on
- Hold down the option key first ( ! ) and then drag the Velocity Slider in the left Piano Roll Inspector all the way to the right
- As you can see in the MIDI Draw Area, the velocity values of all MIDI Notes have been set to one equal value "127"
- While keeping the notes selected, you can drag the Velocity Slider to any value and all Notes will have that Velocity

Here are some other lesser know operations:
- Set all selected Notes to the Same End Point: Select the notes and drag the end position of one of the notes (Pointer Tool changes to the Resize Tool) and then ( ! ) hold down the shift key while dragging
- Set all selected Notes to the Same Length: Select the notes and drag the end position of one of the notes (Pointer Tool changes to the Resize Tool) and then ( ! ) hold down the shift+option key while dragging
Hope that helps
Edgar Rothermich - LogicProGEM.com
(Author of the "Graphically Enhanced Manuals")
http://DingDingMusic.com/Manuals/
'I may receive some form of compensation, financial or otherwise, from my recommendation or link.'