Regions - Feedback

It was fun having more land to build, but when I have filled all the available space in Green Valley, rising to 20K current population 3K local currency, I can’t still see any reason for investing the - ridiculously scarce - expansion items in the region and not in the main city.

These ecological residents require more than ten times electricity, water and sewage than the less ecological inhabitants of the main city! Waste management demand is even higher (111 demand from 22600 pop. vs 176 from 830K in the main city). I have invested an indecent amount of simoleons keeping regional residents happy and I still can’t see any return other than these 3K local currency. 

If I compare the invested simoleons with the return in leafs, the exchange rate between the two currencies should be more than 200/1! But once all residents have their beloved eco market, I don’t see what to do with this precious local currency other than building more eco markets - in expansions I still don’t consider worth opening. So I better go back to my bankrupt main city,

Is this all there is? Am I missing something? Are there some hidden possibilities that will show only at a higher level?