I think that the "note velocity's random" is a great point in the tools of Reason. But I'll suggest to go further with that...
Because when I'm composing without my keyboard, or just when I've already put the line notes, I don't want to remake the notes and chords with the keyboard to give the instrument's way of playing more realism.
So my suggestion is to two other options in the toolbox so we can randomize the instrument's play :
In this picture you can see three note placements on the track. (Yeah sorry, it's all in French but I'll translate some of the words.)
1) The first line is squary, all too much synthetic played, like "too much perfect". And a random velocity is good, but not enough.
2) The second line has applied a length randomization thanks to an option in the "Longueurs des notes" area (Notes' length).
3) The third line has applied to the second line a decay randomization. With a new area called "Décalages des notes" (Notes' decay), we can improve the way of playing's realism easierly than to play the whole track on the keyboard or to modify all the notes with the mouse.
For piano it would be much interesting for those who doesn't have any keyboard, even with the F4 toolbox. But for me, I would use it for my strings' tracks (for example) as I find it faster and easier to put with the mouse the string's notes over the track than recording the whole melodies on live.
It would be the same for other instruments, though.
So what do you think of this idea ?