While I've never been a "sleever", I've probably played my copy of Arkham Horror 30+ times and the cards have held up just fine. I would say it depends on how often you're going to play and how anal you are about your game components. For my purposes sleeving isn't necessary.
Do you play your copy a lot? How are the cards holding up? Worth it to sleeve?
I've played another gamer's copy TONS of times and I've never seen the need for sleeves. There are so many cards in the game, that the chances of wearing them out are small in my opinion.
While I've never been a "sleever", I've probably played my copy of Arkham Horror 30+ times and the cards have held up just fine. I would say it depends on how often you're going to play and how anal you are about your game components. For my purposes sleeving isn't necessary.
Games
How to resolve AdBlock issue? 
