From my experience playing with this and some user feedback:
- Spaces would greatly benefit from having colours and icons. Then not only could the selector show different (and hopefully more obvious) icons, but the header (or site background) colour could also be changed to the colour of the space. A less intrusive coloured line below the header, possibly combined with coloured text in the spaces selector, would also be fine.
- The benefit that this small patch alone does to UX feels immense. Instead of having to adjust spaces for each and every object I create (which actually reduces usability instead of increasing it), I can switch "modes" or "projects" globally, which means a lot if your instance contains objects from very different projects which are being worked on by distinct groups of people.
- User feedback suggests that the position (central header) and combination with a text (space name) improves usability of spaces a lot and makes it very obvious which space one is currently working in.
- Filtering the page contents to show only objects in the currently selected space might help users switching over from Redmine (which is the majority in our case) to understand the concept.