It can be a nice boost this early in the game but as the eras pass it remains pretty static - for example the prices of districts raises the more you have in the same city, but that bonus from Golden Dreams remains basically the same amount of gold per turn.

It will be difficult to build a the Meroe Pyramid next to the extractor as they can be all over the place. The way the Nubians are currently seems fine to me - they have a strong early game and help you get going as a builder/merchant.

I need to try them out. I keep hearing about Nubians and Khmer are either broken or just OP. I just tried the Khmer and yeah.... they are at least OP. Their yields are utterly ridiculous. 

Egyptians are better, in my opinion. It does seem that production-based cultures, in general, are easier to win with at the moment.

Forced Labor doesn't really scale well with Agarian cultures because you can only gain a maximum of 1 pop per turn (and, if you spend them, you need to build them up again). Likewise, buyout costs scale with the number of turns required to finish a project, so Economy cultures still need production to reliably function.

So, it really doesn't appear that purely food-focused or gold-focused cultures are really viable from a strategy perspective (without either making it possible to grow more than 1 pop per turn or setting fixed buyout prices for each piece of infrastructure/district).

Nubian is not purely gold-focused .

You won't buy a few districts per turn, that much is evident. But you can rush buy a few Makers' quarters close to mountains and get some pretty good production going. If you use Forced labour every 3 or so turns it can have a pretty good boost effect. And then in the Medieval Era you pick the Khmer for that Food/Production mix. ;)

This can pretty much put you ahead both in population and production pretty fast, especially with an Agrarian culture.