Actually, in 0.951, I've really started to see the impact of population in my games. No longer is it a 'bottomless void' to be filled. The growth has been capped really well. In addition, the additional population you receive from combats accelerates your cities expansion and further caps your population. you need to consider growth strategy now.
Taxes definately need a tweak though. Having them directly tied to production isn't the way to deal, imo. I'm fine with that being the end penalty of unrest, but there should be incrementing penalty per turn for too high of taxes. There should also be incremental benefit per turn for too low taxes. Thus, if you wanted or needed to run your country a certain way, there would be trailing consequences.
For taxes too low: maybe improvements 'downgrading' or roads falling apart, or population growth too quick (which can cause a disease event to occur), etc
For taxes too high: increasing unrest, workshortages, outright rebellion, population decrease.
Taxes should also not be hit/miss. Each level of tax rate should have pros and cons; and it should be up to you as the player to weigh and consider what consequences you are wanting to deal with.
perhaps as Magnar, you like you taxes high, cause anyone who rebels...you just turn into slaves?
perhaps as Tarth, if you have enough 'over population' you have a chance at producing a free pioneer?
Stuff like that...