I have read some articles about vicky, it is in Chinese, if you are interested I could PM you the source.
I could summarize the article in a few points.
Fact #1: POPs demand is based on your commerce tech/industrial tech, NOT consciousness.
Consequence: POPs generally demand more things later in game.
Consequence: POPs need more money to buy good if you are advanced.
Fact #2: Goods cost money for POPs
Consequence: POPs are more likely to run out of money if there income does not improve.
Fact #3: POP income is related to your economy, the more money you make, the richer your pops.
Consequence: An underdeveloped country (or more precisely, non-industrialised) would have POPs earn less money
Consequence (#1, #2 and #3): A non-industrialised nation, yet with high commerce/industry tech would have poorer POPs
Conclusion: An economy that does not match with the tech-level would suffer from poor POPs, thus difficulties with capitalists POPs accumulating money.
Solution/Suggestion: State Capitalism/Planned Economy is the way to go for countries that try to catch up in economy while having relatively advanced techs, subsidizing capitalists through negative tariffs also helped.
Personal Comments: So, this makes me think that the best way to play in Vicky is not to have your POPs(especially national ones) working at poor RGOs, for example, Grain, fruit, tea or just any RGOs that have low resources value. Put those POPs in factories instead. Non-national pops produce less and thus contribute less to the economy, so it is a bad idea to have high non-national population unless the RGOs they are working in are really rich. Conquering every country possible is a bad idea (unless intented). I could suspect that, releasing some countries as satellites might actually make your POPs richer and improve your income/help lower militancy.
About Profitable RGOs: Coal, Fish, Iron, Precious metal, Silk, Wool, Opium, Oil, Cattles, Sulfer ----------- All these are quite profitable, especially wool in late game make ridiculous money.