The basic idea is that all the decorations (statues, benches, flowers, other deco) and every building that don't cost license should have its own currency, like points, for which the merchant would buy them, and for those points, it'd give other decorations. Like if you have a lot of witch towers, you could exchange them for points and buy a lot of benches and flowers. Or the other way round: exchange a lot of christmas trees and raving rabbits into a white castle.
I know I can sell them in TO but they don't have much value, and there are so many of them that they aren't worth it. On the other hand, the MA boxes were too expensive to just squander Christmas trees and pavilions for 10-20gc when a noble deed of similar gem value is around 500gc. With this change decorations and other buildings would be more interesting.