Since both of you misunderstood my example I suppose I wrote it poorly. You both missed the point where I said you also needed many customs houses. The example is that you build factories in the far east to up supply; you then then spam customs houses throughout your realm to increase demand. Then you have the conga line transport the wealth home.
You could get far more than an extra 0.5 ducats a month from the supply/demand system.
I got your point with custom houses. I just didn't mention them because I was summarizing. Like, manipulating prices = building stuffs. Mainly. I don't find this system to be of much interest. Other than that, you had convoluted maneuvers such as converting provinces to Islam in order to sink the price of wine and cut your rival's income... but that's a bit too situational, isn't it ?
I was aware of there being a supply and demand system, but I'd refer to oblio's post here for my feeling on it :
The number was an exaggeration, I understand that by properly using the system the delta could be much higher.
However, you mostly care about money when you're small. And when you're small you can barely build a trade fleet, buildings boosting production don't exist yet (they're probably 100 years away), and even if they were available they'd be too expensive to mass build. Controlling the right provinces is hard since they most likely belong to strong and/or faraway states.
And once you do reach the spam production buildings stage it's just more efficient to just conquer anything you can.
You could play a peaceful trade game but a peaceful game of EU4 is a snorefest.
If you're starting as a large country things are just fast forwarded by 100 years. Go conquer and you'll make more money than by super optimizing trade.
That's pretty much it. When you're small, you don't build manufacturies. That's a huge amount of money and it's better spent elsewhere, aka in the upkeep of your military or colonies. The return on investment of expensive stuff is unsure and thus hazardous. So, there is little you can do to impact prices when they matter.
And when you're big, with a long trade route set up from Malacca to your collecting node, you don't really need that extra money. Sure, you can take advantage of it for optimal gameplay, but you don't need to min/max by that point.
That being said, I fear, just as you do, that the new system may end up being pretty much bland.
However, it may also be the opportunity to implement events and decisions that would really allow small trading nations to influence prices. That would be great. Such nations were more interesting to play in EU3 because you had to keep dominating centers of trade by sending merchants there. Even when not waging war, you had something to do : overseeing CoT. Now, in EU4, small trading nations don't have much to do but expanding to the right places.