We really should get some legit wonder info out here. It would be good to list what actually makes the miracle better. I know for a fact that you can get lightning powerful enough to destroy ROCKS and custom landscape rocks(pillars?) in the game, with one shot("INDIAN POWER ┌( ಠ_ಠ)┘").
Also I actually played an online match the other day, built a large Norse wonder (yeah, just one, it was big though). In the other village by the coast, I ended up w/ ~640k food in the store, took some to my other village, came back for more and there was 750k food in the store, the town was only ~40 people. My wood miracles were giving me 44k wood per cast. Food miracle wasn't on the map but the creature's food miracle was more powerful than normal, I'm guessing low at 2-3k since I wasn't exactly watching.
I've noticed that WATER miracles get more powerful too, but only been able to see results from one aspect of it's abilities. Simply, the water spells power to cool down the temperature of objects increases many times over and it becomes quite easy to put out huge rock pile fires with 4-6 casts of water, w/ a big Norse wonder. The practical benefit here is that you can use one miracle to quickly put out over 5 burning buildings if you. Also burning rocks take quite a bit of cooling if they are large enough, which become no problem after said large wonder.
Have not tested with miracle water increase yet however.
I'm going to try and experiment in my games to see what things do, right now I'm running patch 1.3 and I will later get to CI things too so maybe I will compose a list. I don't think I'll put much time into specific # values for things though.
Of course.. someone could mod a map and test these things but I feel like blowing a few hours playing instead of coding script.
Note that patches probably make a big difference because I have NOT ever noticed fish farm yield playing black and white 1, patch 1.2 or 1.3. I only got it in a Creature Isle match and haven't really messed with the CI single player yet.
Edit: I've also played some w/ the Celtic miracle and observed it's power through actually a custom creature on a downloaded map.
My experience with it: I built it on land 3, so I had the storm and forest miracles available to me, which ARE affected by it, no increase/extreme storm and I didn't test every miracle in the game since the map doesn't have it.
On a map I was set against an opposing god with a massive Celtic miracle. Soon after I started the map his creature came to a village of mine and cast what either increase or extreme storm, I couldn't tell. The lightning struck at an obscene rate and the storm lasted out for a big longer than expected(~x2?).