As far as the mountain halls goes, mine is level 17 and it adds 100 percent bonus to my basic goods.
For example, my planks is at level 31 and it gives 6750 in goods for a 3 hour run. If you hover over that big green number (in my case, 6750) you will see that it gives me 750 in basic, regular production, and 5250 in relic boosts, and then an additional 750 in "wonder boost" from the mountain halls. That's what they mean by 200 percent.
If you count up every factory that I'm earning that boost on, it adds up to quite a bit. I have 6 planks manufactories. That's an extra 4500 every three hours right there. Then count up my 5 silk, which give me 920 extra from the wonder each (920 basic goods, plus 920 from wonder, plus 6440 relic boost) and count up my 4 dust, which gives me 560 extra each from the wonder boost, that means I'm getting a total of 11,340 free goods every three hours from that wonder, not to mention the 46000 plus pop I get from it ... I'd need three leveled magic residences to make up for that (or more than double reg residences). I'd say that's pretty significant. And that doesn't even cover my sentient factories. I'll never give up my MH. In fact, I really need to level it higher.