So I think part of the problem with Strategus is that people don't really know where the major economic bloodlines are. Clan X wants to war with Clan Y but short of roaming around the map sitting in various castles for a week at a time and then logging in every 30 minutes to look at the map, you probably don't know where their supply lines are.
And it probably shouldn't be THAT hard to figure out. I mean any coin with any village along the way to ask, "Hey, you seen any big wagon trains go by here" would probably do it. Or maybe just look for the road with all the deep ruts in it.
To that end, I suggest that caravans of, say, 100+ crates, leave tracks on the map. You should be able to wander around, find the spot with tracks all over the place and go "ah, I guess this is the local bloodline".
Another idea would be to just build roadways into future maps. If you have 100 crates or more you must move on a roadway (if you end up with 100+ crates outside of a roadway, say, after a battle, then you are reduced to 1/10th speed until you hit a roadway). In this way, long trading routes would be somewhat more predictable.
Basically I think the trading idea is still the right way to go but I think the "raiding" aspect isn't being utilized as much as it should be, probably because there's no clear idea of where big trading caravans are happening.