How did ATC procedures and airspace structure change after San Diego PSA collision?
The recommendations from the NTSB report are: 


  
  Implement a Terminal Radar Service Area (TRSA) at Lindbergh Airpot, San Diego, CA
  Review procedures at all airports which are used regularly by air carrier and general aviation aircraft to determine which other areas require either a terminal control area or a terminal control radar service area and establish the appropriate one. 
  Use visual separation in terminal radar service areas only when a pilot requests it, except for sequencing on the final approach with radar monitoring. 
  Re-evaluate its policy with regard to the use of visual separation in other terminal areas.
  


The most direct change stemming from this accident is the establishment of a TRSA at Lindbergh on May 1, 1979. (It is now a class B area).

Also in 1979 the Lindbergh tower was equipped with some upgrades, including minimum safe altitude warning and conflict alert enhancements.

The other recommendations are fairly vague and I find no indication what, if any action was taken on them. 
But as Gerry pointed out in comments, this accident put emphasis on the FAA's effort to create TCAS.  From the TCAS II V7.1 Intro booklet:  


  In 1978, the collision between a light aircraft and an airliner over San Diego served to increase FAA's efforts to complete development of an effective collision avoidance system.


The see-and-avoid system is still very much in use. Visual approaches are still used. There really were no immediate systemic changes made in response to the accident. Mostly it was just airspace configuration around KSAN and enhancements to the radar system there. But, like every accident, the NTSB and FAA learned from it and took steps to improve safety. The FAA releases pamphlets appropriately titled, "Lessons Learned," about what can be taken from different types of accidents.