I thought that whats prestige for?!
Positive prestige = people are happy = city grows
Negative prestige = people hate the city = people look for greener pastures.
It is much more streamlined, but i like it much more then Civ convulted mess.
This was my take on something Frogboy said in the past. Think of Prestige as the "Standard of Living Index"
0-1 = Poor L0 Usually only exists in Hamlets that are just underway.
2-5 = Not bad. L1-L2 Enough Food and Housing. Perhaps some Pubs and Educational Institutes may be in place.
5-10 = Now were talking! L3-L4 Street parties, coin abounds, with places to spend it. Huge Festivities on honored days and Mansions and Villa's abound. (in the South end of Town at least)
10+ = Good Times Baby! L5 Golden streets, no taxes, all politicians have been eradictaed. Life is just too good to be true... LOL 
Now if a L5 City somehow gets down to 2-5 levels, folks may start looking elsewhere, even to the cities of your neighbors.