Ability to hide spaces from spaces list

I would like to have the ability for users to hide spaces from the list. Once a new message is present in the space the space would re-appear on the list until the user selects to hide it. Or maybe there could be a configurable auto-hide feature that hides spaces that havn't been used for X amount of time (days, weeks, months).

This would allow people to clean up their spaces list, but still allow them to remain a member of the list and thus search for the space.

We have had problems with people leaving announcement spaces simply because they want to clean up their spaces list.