For each level you get to (gold, silver, bronze etc) you get a different model of all the versions of Tom Nooks shop to display in your house. The first model you get is how the shop looked when you first started the game, the next one is a model of the shop after its first upgrade etc etc.
Saving up points takes a while too- you get points everytime you buy from the shop so whenever you get the "points specials" buy everything in the shop, even if you dint need it to get your points up