At this point, as I am not a programmer, I don't want to assume anything is too easy, I would rather assume something is hard than anything.
Another thing to consider is scope of this system. If you haven't heard the word "scope" used in this context it basically means the size of the project.
If this system is really big and complex it takes more resources to complete, meaning people and time which could potentially take away from say, creating the next Episode for a time. These may be extremes but when I tend to think about designing things I find the best way is to figure out what is core to the system and how we can make it as small as possible while being useful/beneficial.
While filtering things could be an answer to stopping trading possibly breaking quests or causing confusion, maybe what it is trying to fix isn't really a big problem?
If you can trade as many cogs for other useful items to create the crafted items yourself I feel like that fixes the 999 cog problem as well as not having a hard time getting materials for crafted items problem.
This is definitely not me saying anyone is wrong, just trying to add another point of view and try get in the mindset of what a designer may be thinking.
I'm with your guys, I would want to trade everything haha!