With the store, I think that improving its look over time with different materials would be cool, it shows the progress you as the player have made over time as you become a more savvy card seller. The look would go from a rinky dinky scrap wood stall to something looking like a really nice kiosk or something along those lines.
You could even have stages of progress, where maybe paying the loan shark back is like a chapter 1 end, and then in the interim between chapters, you could upgrade your stall with new materials, items, and details.
Along those lines, what if you could "level up" after a certain time, and upon level up, you could choose a new upgrade that helps influence your haggle price, update your stall to "charm" the kids on the playground to offer better deals (or intimidate the bully, etc), or provide some other benefit. Now, this might be stretching your basic mechanics or gameplay too far, but I hope it's good food for thought!