There are two ways to get a Kickstarter going. 1) Get more backers or 2) Get the more money from your existing backers. Regarding the second, the quantum costs of jumping between sets is high enough that most backers would come in at one level and stay there. That creates a ceiling on how much money that you can get from your existing backers. However, if you add paid extra goals, you can entice people to spend more or to grease the transition from one number of sets to the next. I'm honestly surprised that there weren't more paid add-ons from the start. The biggest problem with paid add-ons is that they need to be different enough ("Look Cthulu!") that someone who already has three or four sets coming would be enticed to splurge. Ideas for add ons might be something like a 2x2 or wall piece in the shape of a cavern, a double door, or dungeon furnishings like stairs. This kickstarter is a definite value ploy, but it is missing something sexy to kick it into a higher orbit.