What you have proposed is very similar to what actually happened in the San Fernando Valley from the 70s through the 90s, mostly minus the transport part.  When we moved to Van Nuys in 1980 many of the major streets, the ones with four or more lanes, with or without medians, were zoned R1--single residence dwellings.  Others were zoned C1--commercial.  

Then the city rezoned the property along the R1 major streets to R4--multi-story dwellings--apartments or condos. The population was growing, and there was a finite amount of buildable space.  Many of the new arrivals needed apartments and couldn't afford to purchase a house in the L.A. market.  Homeowners were either happy to sell or had their grief assuaged by the premium that apartment developers were willing to pay.

Since then L.A. has invested in heavy rail and multiple light rail lines.  They have added dedicated bus corridors and they had Freeway Flier Busses by 1990 that left from a few select locations where there was available parking and ran to downtown.  My son took these buses while in college.  Most of that clientèle wore suits and carried briefcases.  The areas around transit stops do undergo redevelopment to greater density, if they don't already have high density.

But the neighborhood associations are a real problem.  The other problem is getting from the nearest station of stop to your final destination.   The transportation equivalent of the communications system "last mile problem."  Perhaps gas at $5.00/gal and rising will concentrate the minds of enough citizens to enable a solution.    

As the Dutch said while fighting the Spanish: "It is not necessary to have hope in order to persevere."