Actually, from experience, increasing supply and demand doesn't change the actual prices.
Proof of that can be found in many of Mahon's control systems, where Industrial stations produce up to 6-8M supply of agricultural equipment and yet remain in 2/3 supply levels shown. (our control system bonuses work, our exploited systems don't) Based on them, we should have control systems that provide the cheapest agricultural equipment, but none of them already had a maxed out supply. Contrary to that, we do have a system that provide some of the cheapest agricultural goods, Marralteki, which had maxed out supply for some of them. Even this one didn't get everything maxed out after the x4 modifier was applied, even though it should.
Kinda silly and weird, but it seems to only slow down how fast players can dry out the prices.
Same with Torval, only the stations that already had maxed out slave supply get to retain it and be the most profitable.
I think the whole thing is in the fine print. The bonuses say "production and consumption", not "supply and demand". The status quo is unaffected.