Caravans at the moment only provide a food bonus. So whether or not you use it on the AI, or on your own city, it does not matter. Hopefully, with time it can provide more bonuses, but basically if you hover your mouse over the caravan once it's doing its route, you'll see the % increase in food.

My biggest problems with Caravans right now, is there's no way to protect them from creatures if they get attacked, but someone did mentioned that if you group up the caravan with a little escort before actually establishing the route, the escort stays with the caravan forever, so I still have to try that to see if it works.

Are you sure it's just food? I set a caravan up for a ridiculously long journey and once the route was finally established I noticed I was earning quite a bit gildar more than before. The money bonus might just not be displayed.

However I didn't reload to double check if it actually was the caravan which boosted my economy, so idk.

is it me.. or are they sort of 1 directional?

as in... if you look at the screen at the starting city, you'll see the destination name and the % in the relevant section

but when you look at the destination screen.. the starting city name will show up with something like (no caravans sent) or some such

would be nice if there's an option to auto build caravans that got destroyed instead of having to figure out where it went, etc. even better.. keep the route and just not get the bonus when the caravan is destroyed.

Not sure if there is any bonus from it but you can have city_1 send a caravan to city_2 and then also have city_2 send a caravan to city_1.

On a related note, how do I set up a route with an AI?  The AI in question has even asked me to send a caravan.  I have a trade treaty with them.  I've sent a caravan from one of my cities but I can't find the button (or mechanic) to allow me to establish a trade route.  

You establish those trade routes in the same way you establish them between your own cities. Produce a caravan in one city that still can do so and send it to an AI city instead of one of your own.

As to the benefits of doing so? Apart from a road for a quick invasion or a food production bonus on your side of that trade route ... none to my knowledge. Or is there some hidden diplomacy benefit that just does not show anywhere? Or more value/output on your side of the general "trade agreement"?

Rabenhoff

In regards to establishing trade routes to other cities:  I did that.  I literally moved it onto every square in the AI's city and it would never "meld" or otherwise indicate the route was established.  So I think there may be a bug, because I gave up on the AI city and decided to just move it back to another one of my cities, and it wouldn't establish a route with my city either.  Thanks for the 411 though.

I belive that is the time interval between people that use the trade route, Ie traders. I dont think the caravans themselves respawn, i think technically the 5 turn respawn is kind of like "trade has sold all goods now going back" Vs being destroyed by a hostile, if destroyed that trade is toast so you need to make a replacement trader.

This is the kind of lack of polish that sadly this game is being ragged on with, it should be clear what bonuses an upgrade gives.