Hmmm the mood meter is sometimes in the lower part of the green for myself but it's never been yellow or orange since the update. The only time my sims mood meter was very low was when she had the shy trait and she was in the middle of town surrounded by people. I wonder how many others are experiencing this low mood problem?
My downtown area of bridgeport is always near empty except for the theatre and waylons place they always seem to have sims scurrying around, beyond that I only ever get one or two sims beside my own where ever I go. I'm sorry I can't really help but I'm sure someone may know of a way...good luck and I'll keep my fingers crossed