I'd only see a point in raffling picks 1, 2 and 3. Any further than that is pointless really.
The only reason to raffle is to prevent tanking for the top pick. Mix up the top three, and the three crappiest teams in the league still get the three best picks, but a team can't guarantee that they'll pick up the best player.
Maybe even the first 5 picks, just so teams around that area have absolutely no incentive to tank.