With SPI, you switch Civics continously, almost every 5 rounds at some part of the game, no Golden Age lasts long enough for that period. You're just not using the traits full potential.
Also: REP + Buro + Caste + Pacifism gives the most research. Towns need way too long to mature, but in rare cases so very long games and with a bad capital, Free Speech can be better.
Settling GPs is very bad and cannot be compared towards the other options, usually the special ability and bulbing are way stronger.
Also, Coal Plants and Factories without enviro are no problem. Keep cities small, run Biology Farms, use the Kremlin enhanced whip. That's the most efficient form of production.
And of course, decisions matter, it's a strategy game after all. One needs everything and commits towards a path, but that path is way more complicated then you make it sound, one needs Farms, Cottages, Mines, Windmills, Watermills, the full arsenal.
Only improvement I only build in one city are Forrest Preserves, and I generally don't like Lumbermills because chopping + Workshop / Farm / whatever is better in 99% of the cases.
You're just very fixiated on one playing style, but if you went deep into the single decisions, like "which improvement do I build next" you'd see that you're hurting yourself with every "always" rule that you have.