Well I don't think we're all thinking on the same scale.
First off, I don't think their should be territory caps. Here's why.
You can build a power plant anywhere. It's just easier if there is coal there. That settles energy resource.
Iron accounts for something like 20% of the earths crust. If you can't build more steel mills and dig up more iron, then something is wrong.
Oil. OK yes, technically this is a bit harder to explain away. But what we could do is say that you can only improve the territories that already HAVE existing stocks of oil on the map (similiar to improving IC in that regard).
Rubber, rubber is no longer rubber, it's rare materials. rare materials are found everywhere, it's just that each location generally has differant rare materials.
Now I'm not saying that the territories should improve substantially. But then again, if you invest more energy into improving your power production infastructure, then hey, shouldn't you get more out of it? So yeah, it's something I'd like to see happen. Also the ability to add resources to a province thru a event would also be nice for modders.