The only real influences of John Forester that I recall were in influencing the writing of the vehicle code for California (copied extensively) that outlined that cyclists need not cringe in the gutter on roadways where that would invite dangerous passing by motorists (Okay, it was worded a bit differently.) and in articulating to new cyclists how to ride like the "club riders" from which he was spawned. These contributions likely forestalled the end of the second bike boom in America, but probably not by much (1974 is still the biggest year in American history for bike unit sales).
The segregationist folks have now held sway for nearly twenty years. We're still looking at national bike commuter numbers of 0.6%. New York City, which spent boatloads to implement segregation under Bloomberg, has about 1.5 times the national average, not exactly a glowing success, especially when compared with Davis of the 1970's/early 1980's where bike trips outnumbered car trips without much of any infrastructure (a handful of bike lanes and one bike path).
These fights over the supposedly powerful VC bogeyman are lame. Few enough people ever heard of VC until the rise of the segregationists, who needed a bad guy. Sure, Forester's personality makes him a great bad guy, but he really didn't affect history much. Had he never existed, all we would have seen is a slightly, probably unnoticeable, quicker decline of cycling in the 1980's and vehicle codes that make it near-impossible to bike tour or ride any real distances.