I was just thinking of this myself. Perhaps the other factions can request specific items as well, like food or weapons. Thus you are still giving them something, but instead are giving up more easily obtainable things. Right now the only ways of gaining more silver are praying for a crashed silver transport or milking traders as they pass. However, I'm really miffed with the state of trading right now (mostly lack of control, can't manually send/set limits on what goes into your "trading" stockpile).
Personally, I'd like there to be some type of "overworld" where you could see the other nearby tribes/settlements. The idea is that you could then interact with these settlements. One idea is that you could send a trade mission over to them, where you would load up with certain goods and offer them for others (perhaps a relations boost?) The people would be gone for a few days before returning. You could also send an "ambassador" to another settlement to talk up relations. This would require high social skills/take several days. If nothing else, the ambassador could just pick up the mood of the colony (what they need/want, open to any trade, are they thinking of attacking, etc). Maybe you could send scouts as well, or set up some relay/sensor stations to pick up movement. You could notice a group of pirates about to descend upon another town, and tip them off for a relations boost (and then offer to send help for more). Orrr.... you could raid other towns yourself! You could then raid the raiders, or attack the other settlements and specify goals (steal food/weapons/silver, capture colonist, etc).
Personally, I'd like there to be some type of "overworld" where you could see the other nearby tribes/settlements. The idea is that you could then interact with these settlements. One idea is that you could send a trade mission over to them, where you would load up with certain goods and offer them for others (perhaps a relations boost?) The people would be gone for a few days before returning. You could also send an "ambassador" to another settlement to talk up relations. This would require high social skills/take several days. If nothing else, the ambassador could just pick up the mood of the colony (what they need/want, open to any trade, are they thinking of attacking, etc). Maybe you could send scouts as well, or set up some relay/sensor stations to pick up movement. You could notice a group of pirates about to descend upon another town, and tip them off for a relations boost (and then offer to send help for more). Orrr.... you could raid other towns yourself! You could then raid the raiders, or attack the other settlements and specify goals (steal food/weapons/silver, capture colonist, etc).