I made a similar thread a week or so ago and I think most people agreed that population is clearly much more marginal now. They have increased the capacity of cities from 8 to 16 in the beta patch so that will cut down on the amount of cities needed to hit a significant pop (and hence save farm land too). About the only issue left is Morale and I'm sure that something will be in the works now to compensate.
On the plus side for Population now, you get that full Raw Production applied to EACH function (Social Construction, Military Construction, Research, and Income). In stock GC3, you were really just dividing that larger number (but had the flexibility to push it all to one function or another as you chose). So I don't think the total output has declined too drastically, but the diminishing returns do kick in now (probably for the better).
I'm trying a higher pop game now to see how it feels compared to just keeping the pop at 4 or 9. Hopefully I'll have a better sense later in the game.