Currently we can call traveling merchants in, as long as you’ve [literally] piled up enough wood or clay. They actually show up in the world!
Other than that, they don’t have any good sales, they leave eventually, there’s a cooldown, you don’t want goblins to kill them. I feel there’s a lot more that could be done with them. They look like Hearthlings, after all; why can’t they act like them?
What if you could spare a bed to have a traveler stay the night, possibly offering better deals if your hospitality is good enough?
Or why limit it to merchants? Maybe an adventurer or soldier could come through your town, needing rest or a drink. Maybe one needs supplies, promising a share of the loot if he makes it back. Or maybe he needs to lighten his load, selling what loot he has for a reduced price. If soldiers are visiting your settlement and a battle breaks out, they might help if they’re in good enough shape.
More ideas for travelers, each one crazier than the last:
A wandering apprentice could help your crafters when she’s in town, simply speeding up every recipe.
Guests could come in on feasts and festivals. You better have a lot of extra food ready, or morale might take a hit.
Pilgrims for Cid could come through, cheering your more spiritual Ascendancy Hearthlings if you donate supplies.
A group could come running for safety. Do you help them, and risk danger for your settlement?
I don't think this mechanic needs to be taken as far as it can, but I'd like a little more. Inns seem totally in character for Stonehearth - I like to build them every so often, at least.