Available Upgrades Option for Buildings in Town
I think it would be incredibly helpful to have a tab, (button, section - whichever works best) in your town that allowed you to see what buildings are available to upgrade based on your current collection of items.
Currently, you have to click on each building (and the train) in the town to see what items are needed vs how many you already have.
Having a section that listed the available upgrades would eliminate the need to click on each building individually. Additionally, it could be used as a main hub of sorts to implement the upgrade from that very screen.
Being able to see each building and the corresponding required items to upgrade could help a player who is hoping to collect items for more than one building at the time.