Sounds okay. 

Need to test it for useful feedback.

What I like about workspaces is that they have (at least) 3 functions from the UX point of view:

1. frictionless input of code to evaluate (single or multiline)

2. output when doing cmd-P

3. user orientation because it will remember you that you were doing something related to that little code pretty much like that post it in your desktop

I get the point about shift+enter+:  and getting a command evaluated but a cmd+[something]  could open a workspace and you have more features at the same price and one keystroke cheaper because you won�t need the : to get something evaluated.

Plus you�ll have to added friction to do something multiline (like a Gofer load for example)

You may say, hey I don�t want pollution on my desktop, fair enough you have cmd-w to optionally close it right after use. 

That enables a pretty good flow*

Hey� I have no complains if it�s there

just sharing how I use workspaces 

*which BTW is interrupted (so broken) by not having the �open new workspace� key combination as many smalltalk IDE have (so your flow forces mouse-menu-click before unloading the code of your next evaluation) <- it�s only me or that sounds like a quick fix of high return?