I am suggesting an overhaul of the trade system currently used in Sins in favor of a really well implemented one I've seen in another space rts.
In Star Trek Armada II, trade worked like this: You payed to build your trade ships, and your trade ships would actually carry goods, and if your ships were destroyed, those resources were lost along with the costly ship. For example, say each trade ship in sins would dock with the trade port, then load up on X credits. If that ship were destroyed enroute to the next trade port, you wouldn't get those credits. Ally tribute worked in the same manner. If you wanted to send dilithium crystals or crewmen to your ally, you would select some trade ships, dock them at the port, and then load them up with the crew or resources. Then you'd send the convoy to your ally, but it had to be protected because it could be destroyed. Right now you can only "wire" resources to someone. As it stands, disrupting trade is not a useful activity. But it could be! Imagine the fun of having to protect trade convoys, not only because they contain resources or credits, but because you had to buy each ship. Refinery ships could function the same way...you have to buy them and their loss becomes actually costly to you. And to prevent spamming trade ships, what if each trade port raised your trade ship population limit, or each refinery raised your refinery ship population limit? What if the TEC, with their "better economy" got +3 economy ship limit per trade post and everyone else got +2?
Now combine this idea with the way trade is implemented in AOE2. You have economic buildings (the market and dock) and economic units (the wagon and trade ship). You assign an economic unit to one of your ally's economic buildings. It will travel to this building and then back to one of your own, and each time it returns it will offload gold, the amount being based on the distance it traveled. What if in Sins, you could select your trade ship, and then assign it along the trade route it will travel (using waypoints). The money it will pick up at each station along the route is based on that station's distance (in number of jumps from your home planet (or maybe from the trade port it stared at. Using this system, trade alliances between you and the AI actually become useful! And you can have multiple, player-defined routes, not just one "longest route" that the game hands you. Now you could actually select your trade ships and shift-right click all through your empire and into your ally's, setting up your route of choice.
Just off topic, as it stands, planets may have bonuses such as "penal colony" or "massive pure glaciers". This is similar to the planetary bonus system that exists in Star Wars Empire at War. What if these bonuses instead functioned as "commodities" that could be traded to players in exchange for credits/metal/crystal, diplomatic leverage, or other commodities? What if these commodities had to be sent in trade ships to an ally, making them vulnerable to interception by the enemy?
What if I keep asking rhetorical questions?