I actually think GPL may have put people off taking up real competition driving! Its so damn hard I wonder how many kids thought "If I'm terrible at this I'll never be any good at at real motorsport...."
Some sources suggest DK wanted to include a 'trainer' or Formula Junior option in GPL to soften the blow of but it was rushed out so this never happened... All we got were 'detuned' F1 cars that were still quite difficult....
Having said that I think GPL helped me a bit when I got behind the wheel of a mk II escort for the first time on a loose surface. Stupidly I remember thinking 'wow this is almost as accurate as GPL... no, hang on, this is REAL'