Hi, I'm also experiencing the same problem that your having to nox0r.
Last time I played Sim City 4 was in December; no problems. I installed some landmark/park/street plug-ins last week. Tested them out, worked fine; no crashing. Started a new city. Had some rail ,road, and avenue connections to my sister city. All was fine until I started developing medium wealth residence and commercial in the city. After a couple of months of growing my avenue's started flashing between commercial and residential constantly.
Two things I thought of was One: I have three plug-ins called "No palms,Sidewalk Texture Mod, and Uni-Density Streets" that I DL before. Two: I have a GRL track between my avenue's in my city. Its not a GRL puzzle avenue, but more like “ full avenue;GRL; full avenue” I took out "No palms,Sidewalk Texture Mod, and Uni-Density Streets" No luck. I even took out all plug-ins that I D/L last week; no luck. I tried the city with no plug-ins. It works some, but the Avenue's still flash; not as much though. I don't have to many connections to the sister city, around 7. But I've had a city with way more connections in the past without the flashing avenue's.
Any Suggestions?, Arigato