btw. I made a little census regarding the behaviour of the recent file list in various applictions. Adding only on open wins over adding on open and save with 60% (though my sample size is much too small to give representative results).
But considering that you can't save a project without opening it first, not adding the project on save seems to be the right solution, since the project is already guaranteed to be in the recent list (unless it was open indirectly as a part of a workspace, which is exactly the behaviour we want).