Population

Now it impacts money gain (guildars) and research. Production stays out of population influence.

If you will look in deatails window of city and hold mouse above guildars/research lines you will see short sumary and there will be posted cities name and income from it (it comes from population + city level bonus). In early game it usualy brings more money than your buildings. However research is more boosted by buildings, than the population. Good use of population is sacrificing them to mana by death magic Joking.

P.S. not realy, i actualy love abuse high prestiges with fewer cities and sacrifize population. Never ending mana.

I have not noticed this, unless you mean that city level impacts research (+1, +2, +4, etc...) and I guess income.  But if that's what you mean, then it impacts production as well.

In my opinion, population right now does not play enough of a role, and as a result, the most effective strategy is to have a ton of level 2 cities... Well, if they somehow grow beyond that, it's nice, but not important.

No i mean that behind that city name value is brought bonus from city lvl AND population. I have checked it few times and numbers were higher that city level bonus let alone, so it looks like population bonus is hiden in this numer also, but not shown separately. Of course if you have nerves testing it out i would be grateful, i would like to find out it if its possible, because its important for my strategies.

By the way you need spam outposts, not cities It is enough of 4-5 cities but get tons of outposts around them and claim as many clay mines as possible it will rock your production and everything else then to. I usualy dont care if AI is taking crystal mine or metal, but if i see some clay mines around i try to get them at any cost even starting a war.