First I want to say that I love the idea of workspaces. It's what brought me over to Opera in the first place.
Two features I'd like to request:
Shortcuts for navigating between workspaces when there are more than two (exactly how tabs have "next tab" and "previous tab"). Right now you can only set shortcuts to go to specific workspaces.
Shortcuts for quickly adding and closing workspaces. (ctrl+t but for tabs).