Thanks for your reply.
Not sure if any particular wealth level are creating the problem, though I do have mostly medium-wealth inhabitants. Also, since there are less sims taking up the space usually inhabited by a lot more lower wealth sims, there are jobs that now don't get filled, so my industry basically slows down and goes abandoned. I've tried upping the density, but in the past this effect was immediate, whereas now it takes quite a long time to up density.
I agree that the SC4 system was more forgiving - and I'm sure this will get sorted out in time.
Thanks again -