disable add-ons in demo mode.
Why would disabling add-ons make the demo any more likely to attract people? Letting them try some of the better add-ons would probably *help* convince them to buy it.
People who won't buy it anyway won't buy it, people who will anyway will, that just leaves people who may. How many people would buy the game *just* to unlock the ability to use add-ons? How many would buy the game because <add-on> would be *AWESOME* in multiplayer or with more bricks? Or "I made this great VCE build with only 142 bricks. Now I want to show it to people, but demo can't host"?