I keep a ton of mine sleeved, but not quite all of them. My wife and I both play, so we own 4 Core Sets, 4 Edge of Darkness expansions, and two of each Force Pack, etc. We also play AGoT competitively, so there just ends up being way to many cards to warrant sleeving.
But, you raise a good point in that at least certain objective sets should probably be sleeved up constantly (e.g., Falcon, Han, Luke, Vader, Emperor, etc.).
Edited by divinityofnumber