The listed bonus is the value of the trade route between those two cities. They only get that benefit if there is an actual caravan sent.

It's just listing all the routes that connect one city to another. If you sent a caravan to every city and deleted them, it would show you all the bonuses you could get sending one to every single city in your empire.

I always figured the caravans took a day off upon returning from a trade venture.

You all have it wrong.  What this means is you have a caravan incoming to a city from a different city, but no outbound caravan going back.  So if your city has 5 caravans coming to it, but you can only send out 3 from that city you would see caravan not sent for the two cities that you are not trading back with.

Another example

3 cities sending you a caravan, but you send your caravans to a different 3 cities.  Your city info panel would show 3 cities as caravan not sent and the other 3 cities names only.

This bothered me for a long time and I thought it was a bug in v1.09 something, but it is not and it makes perfect sense to me now.  Hopefully you understand what I wrote above, if not let me know and I will try to explain it a different way.

Sorry about that I should have read your reply a little more closely.  I hate the caravan bug that occasionally pops up that will not allow you to build new caravans for a captured city.  It happens from time to time usually once or twice a game for me on a large map.

i reckon they should split roads and caravans... don't know if it's me or not.. but i think i've seen roads move before.

i think i saw a road change path after i terraformed a short cut around a mountain. but then again, it could just have been coincidence where the new caravan arrived after the land was raised (out of water) and created road there.

so.. you can have roads as an entity.. that upgrades on its own based on usage. (by whatever) and you have caravans that lvls up based on number of trades performed (ie.. number of trips)  don't know.. maybe more profits.. or maybe can evade battle or higher movement rate or something..

...why is that though? for that matter.. imagine a 3 stop straight road. a-b-c... does it make it even faster with 6 caravans? a<->b b<->c and a<->c ...

that's logical.. but is it the way elemental works? do all the different caravans between the corresponding cities show the same numbers for the number of trips/turns/whatever till the road level up?

or for that matter, assuming ab and bc is same distance... and all caravans started off at the same time, do they show the right numbers (whatever they are!)

... if ab's caravan got destroyed and you build another one and send it along the same road.. will the "xp" of ab's caravan be reset to 0 or does it calculate the right number of trips left to upgrade the road?

I would say the easiest way at the moment would be to do a inverse economic starbase from GalCiv2. That is, caravans aren't attackable once set up; they no longer exist as independent units, only as (functionally) counters. Monsters can 'attack' a section of road. If they do, the caravan takes a hit. The longer a monster camps on a route, the less bonuses the caravan produces and the slower road development occurs until finally it stops all together.  A little (monster face)! would appear over any spot that a monster threatens so you can find it easily.

I also have a problem with caravans.  I get a "No Home Found" message when I sent a caravan from a captured city to another city.  The detail text of the message reads:

"The caravan cannot find a path home, and therefore cannot create a trade route."

Any ideas on WTH this means?   

This.  Really hate the micromanaging of Caravans after they've established a route