This was my first reaction too, as i was in the habit of leaving all brown houses in my Pressboard Estates area for visitors.
But I've noticed that I'm not getting an increase in graffiti, like visitors had nothing else to tap, so I've become less concerned about it.
But I'm not leveling up beyond L3. Too expensive, not worth it. Also, the new shockwave tap actually seems to have increased how long it takes me to collect because the effect is so laggy. Boo.
Really a botched attempt to create this shortcut tool. But i love the building, fits well in my town, so i will deal with the minimal down sides.
Besides, there's ALWAYS something for neighbors to tap even if they have to go to KL. So no worries. It's when someone's gone for several days that it becomes an issue.
Keep calm and tap on! =)