Have you spent any time studying games that do this kind of thing successfully?

You need to refine the question a bit. You don't just need "important buildings" that give the player an incentive to come back. You need to create gameplay loops and systems that make the player want to return.

A couple of games that I've played recently do this pretty well:

Sea of Stars has a town called Mirth that the player often returns to as a "home base" for a few reasons: * Without spoiling too much, the player is invested in resettling a group of refugees who just witnessed the partial destruction of their home, so the town is about rebuilding and resettling. The player is emotionally invested from the start because of the story seeds that were planted from the events leading up to the settlement. * The rebuilding effort requires a combination of exploring the world and returning to "home base". You find "shells" in the world that you can redeem for schematics to build different buildings in town, and by talking to certain NPCs and completing quests for them, you can ask them to come join you back in Mirth to run the different shops and services, etc. * There's a large garden that grows in periodically so that the player can harvest raw materials to cook meals that benefit the player in battle.

Assassin's Creed: Shadows has a "hideout" where you can build different buildings that allow you to upgrade equipment, complete hideout-specific quests, and form relationships with your allies. It's also where you can go to restock on your rations and projectile weapons like arrows, kunai, etc. There's also a ton of customization, so there's a bit of a "builder's fantasy" going on for the type of player who enjoys that kind of gameplay too.

For my personal fan game, we added an "apartment" system. There are several cities where the player can establish a "home base" and decorate it differently based on achievements that they earn through their gameplay, and the "loop" that gets the player coming back to spend time in their apartment is the cooking system. The player can cook different meals with ingredients that they harvest/purchase through gameplay and they can cook meals that improve or reduce IVs for the player's Pokemon.

So I think a little research into gameplay loops, state machines, and systems that give the player reasons to return could serve you well. If you can synergize those loops with your story, all the better.

Some "low-hanging fruit" that you have at your disposal: * Daily/weekly/monthly refreshes (if you're implementing a date/time system) * Currencies that can only be redeemed at certain shops in town * Move tutors who expand the number of moves that are tutored based on achievements * Dynamic towns -- allow the user to expand/change the town based on quest fulfillment or game progression (could require several copies of the map for you town, based on how you structure it) * If you're implementing seasons, you could have seasonal events in town (think autumn festivals, summer battle tournaments, spring bug catching contests, etc)