Yes, it would be good to reduce the 'penalty' of loading OW with a large active Workspace.
Aside from caching etc. I'd really like the option to select a Workspace when loading OW, other than remembering the Shift modifier, and creating a new, empty Workspace.
Optionally the Workspaces window would show on launch to select the Workspace to load, a la Opera (which also includes the option to open the 'last session'.)
Perhaps the simplest alternative might be to allow auto-saving of open pages (as a default now) but also the choice of whether or not to automatically re-load the Workspace on launch.
This would make it easier to deal with unexpected browser launches, which often happen with links from apps, e.g. Help files, wherein you only want that single link to open, safe in the knowledge you can re-open your Workspaces when appropriate.
As an aside, it might be interesting to be able to (auto-?)sort the Workspaces list based on most recent use of each Workspace, and perhaps the number of contained pages show in the title.