I built the cheap roads first but I can't figure out how to upgrade them without bulldozing and that always destroys the nearby buildings.
There has to be a better way, right?
Under the road type (straight, curved, etc) there is a turned arrow button. Click that then click a road. It will give the option to upgrade or downgrade. Single lanes can't be upgrade to double lanes and visa versa.
You can upgrade roads/avenues (but not from roads into avenues) with the road upgrade tool. Just click the road building icon and it'll be one of the buttons. I don't know how to describe the icon since I don't know what it's supposed to be, but it's there.
Occasionally claim doesn't work, or does work but will bug you out completely (you lose your identity and ownership of your other regions and can't really do anything until you quit and reload). Seems to be lag related. Most of the time it has worked for me though. I had a pretty big region I jumped around in a lot.
"Compartmentalizing" doesn't actually seem to work that well. It only seems to draw a fraction of population from any given region at best. I tried building a large residential and commercial region, with a large industry only region next door, they didn't link up too well. Some of the people went to work in the industry region, but not enough, so I had a lot of unemployed sims in one city, and a lot of industries shutting down due to lack of workers in the other. This was sticking with basic low tech factories and uneducated lower class sims just to see if it would work.
Region wide demand for all 7 (low/med/high res/com + ind) zones eventually maxed out, just to prove it's not as simple as moving from one city to the next. You can make an industry heavy city and pull in some workers from other cities, but I'd guess at least half have to come from that city itself.