Here's what I'm working with now instead:
Agriculture
High Upkeep
+1 health in all cities
+1 food from farm,
-1 hammers from farm
Conquest
Medium Upkeep
New units recieve +2 experience points
Military units produced with food
-25% war weariness
Extra gold when conquering a city, reduced population in conquered city
Mercantilism
Medium Upkeep (I decided that Low may be too good)
+100% cottage growth
No foreign trade routes
+20% gold in all cities
+2 commerce from village, town
+1 happiness from market
+2 unhappiness from thieves' guild
Foreign Trade
Low upkeep
+25% war weariness (trade is the natural enemy of warfare!)
+1 trade routes per city
+50% commerce from trade routes (You guys are right that +10% would have almost no effect)
-10% gold, +20% culture in all cities
+1 food from workshop
Responses:
Makes cottage-spam even better.
I like my idea:
+2 gold per military unit upkeep.
+20% gold
can gold-rush
-30% science
which makes it a very good "builder" civic.
Yeah I know

. But that is the point. To make cottage spam actually be effective. Without my changes, grassland farms under agriculture could support 1 and a half scientists. These scientists could produce 5 beakers per turn each when under caste system and scholarship and produce some culture and great person points as well. As a result, 100% of the time you should build a farm for the maximum yield possible. Cottages were useless since they maxed out at 5 commerce.
By the way, the civic you proposed is horrible. +2 gold per military unit upkeep and -30% science are too punishing for +20% gold and gold rush. No one in this forum would ever consider using this civic because it is more useless than the current mercantilism civic (adopt caste system and mercantilism as they are currently will get every single benefit with none of the penalties that you suggested here).
Merchant Houses:
No foriegn Trade
+50% gold
-25% lightbulbs
-2 happy theives guild
-50% military unit production
Can rush production with gold
+2 gold per unit maintenence
This version that you proposed is also terrible. A builder civic does not reduce your research rate! When would you ever adopt this civic? When you've researched the entire tech tree and feel like making the game interesting by buying a brand new military that you couldn't afford to keep without entirely halting research? I dare you to try using this civic in your game and see how far you would make it before realizing just how impractical this civic really is.
Your version of conquests was exactly like mine except there is no war weariness reduction in yours.
Workshop food is interesting. Could result in workshop-spam...
Actually it will probably result in workshop-spam. :/
Will it? Or will someone instead make their city as large as possible to take advantage of the increased trade income (understand that larger cities make trade routes more valuable to you and the person trading with that city) and therefore build farms as well in some places. Some places will become farms for people and trade, other places will be hammer heaven, and some may fall in between. At least that's what I'm hoping will happen. And besides, would you be able to choose between cottage spamming or workshop spamming?