There are good reasons for not building all three of them:
- JS Bach's and Cure For Cancer require techs (Music Theory and Genetics respectively) that are no use to building a spaceship. So the player won't research them. Cure For Cancer in particular comes along very late, and if you're building a spaceship, the high-shield cities where you would've been building wonders will now be building the high-shield spaceship parts. If the AI ever researches the techs and the human player buys them, they might build those wonders (JS Bach's in particular).
- The Sistine Chapel is no use to anyone if they don't build Cathedrals. You'll read a lot of threads here that advise players not to build Temples, let alone Cathedrals. So for players who follow that style, the Sistine Chapel is a serious waste of shields!
But what about the happiness issues? Well, the same players who advise you to not build Temples, will tell you to build Marketplaces and secure luxuries instead.
Admittedly those same players will probably never build a metro in a SS game because to do so require Sanitation which is an optional tech and so a waste of 4 turns of research. Having said that, there's nothing wrong with purchasing Sanitation from an AI, and building a few Hospitals where there's food going spare.
Here's a comparison of the two styles, assuming Republic or Democracy as a govt. (i.e. no MPs).
Temple + Cathedral + Sistine + JS Bach's + Cure For Cancer
Cost: 60+160=220 shields/city, + 600 for Sistine, 600 for Bach's, 1000 for Cure
Upkeep: 3gpt per city with both Temple+Cathedral
Benefits: 10 unhappy citizens converted to content per city (8 in cities not on the same continent as Bach's)
Culture: 2+3=5cpt, +6 (Sistine), +6 (Bach), +3(?) (Cure)
On Monarch, those 10 unhappy citizens converted to content will give 12 content citizens per city - but note that the 10th comes very, very, late in the game, so essentially it's 9 (11 in total) for most of the game. Therefore in the figures below I'll be discounting Cure For Cancer.
However a Metro has 13+ citizens, so there'll be at least two unhappy citizens. These must be balanced out with "Happy Faces", which turn content citizens into happy ones. There are four sources of Happy Faces:
- Luxuries. Each luxury hooked up generates 1 Happy Face. Marketplaces multiply the effects with more than two luxuries.
- Entertainers. Each citizen turned into an entertainer generates 1 Happy Face.
- Luxury Tax. One gold generated by the Luxury Tax generates 1 Happy Face.
- War Happiness. Provides 1 Happy Face per 4 citizens per AI that declares war on you, up to a maximum of 4.
There is another way to remove unhappy citizens:
- Turn them into specialists, as long as there is enough food to support the population.
For a size 13 city, with 11 content and 2 unhappy citizens, 2 happy faces are required. That's 2 from luxuries, or 2gpt from Lux Tax, or 1 entertainer (1 unhappy becomes the entertainer, leaving only 1 Happy Face required), or 1 war declaration (13/4 = 3 rounded down), or any combination of all four.
For a size 16 city, with 11 content and 5 unhappy citizens, 5 happy faces are required.
That's 5 from luxuries (either 5 different, or 4 with a marketplace), of 5gpt from Lux Tax, or 3 entertainers, or 2 war delcarations (3 * 2 = 6).
Marketplaces
Cost: 100 shields per city
Upkeep: 1gpt per city
Benefits: +50% tax income, multiplies the effects of luxuries for each connected resource after the 2nd.
Culture: None.
Back to Monarch, our size-13 Metro now has 2 content and 11 unhappy citizens. To stop the city rioting, 11 Happy Faces are required. (Each unhappy citizen requires 2 Happy Faces to make it happy. Happy Faces make content citizens happy first, so those 11 Happy Faces will give 2 content->happy + 5 unhappy->happy = 6 happy + 1 content + 6 unhappy citizens.)
Where do we get those 11 Happy Faces from?
- 6 luxuries (each Marketplace will generate 1+1+2+2+3+3=12 Happy Faces)
- 11gpt from Lux Tax
- 5 entertainers (meaning 26 food from 8 citizens plus city centre - good luck!)
- 4 war declarations
- Some combination of the above.
For the size 16 city (2 content + 14 unhappy), 14 happy faces are required:
- 7 luxuries (1+1+2+2+3+3+4)
- 14gpt from Lux Tax
- 7 entertainers (32 food from 9 citizens plus city centre!!)
- 4 war delcarations
Conclusion
The first style requires fewer luxuries to be hooked up. This means less pressure to secure sources through trading or war. It costs more in terms of shields and per-turn upkeep. Most cities will probably have Marketplaces anyway.
The second style relies heavily on luxuries, and early on, Lux Tax. This means more trading, or, perhaps more likely, war in order to secure those luxuries. With 8 luxuries (=20 Happy Faces from a Marketplace), a Monarch metro can reach size 22 without the need for additional input in the form of Lux Tax, entertainers, Temples, Cathedrals, etc.