I'm sure the mechanic of new cities starting with modern infrastructure has been talked about a lot here.  I have two suggestions for how to improve this:

1) Discount Old Infrastructure.  A tech in each era should reduce the cost of all infrastructure from previous eras.  This should be additive so that really old infrastructure gets multiple discounts.  This will make modernizing old cities easier (as it should be), and will discourage people from destroying old cities just to rebuild them.  

2) The "free infrastructure" for new cities should exclude infrastructure from the previous era.  It's too overpowered right now given the placement of the tech early in the era.  It should only give you really old infrastructure, not everything up to that point.

I prefer the "let settlers apply all the infrastructure to old cities" solution. Way more elegant than your proposal. Probably easier to implement too. 

I like the one dudes let settlers add the infrastructure idea. In reality though it's not hard to have all the things by industrial era cuz you end up just using them (the infrastructure build) to fill turns while your cities do nothing. And alot of them are completely unnecessary until you want to use them as turn fillers anyways.

ErichVonKlick wrote:
until you want to use them as turn fillers anyways.

Well, you can always use ceremonies for that, too.

I feel like this fits well in the game design category. I personally do not think that the production cost should increase over time. It's like.... Did we get worse at making stuff?? :)