I'd guess that CA could well be one of the steeping stones that might help those who are still basically 'tonally retentive' but are interested in dabbling their toes in something more advanced - not everybody is willing to take a flying dive into deeper waters, after all.
I think that I'd very much fit that description, Ron, although for me it was the 3rd Piano Concerto
'Gift of Dreams' and
Autumn Gardens which were my entry into the world of Rautavaara, after hearing the second movement of the concerto on a Gramophone CD. I've bought several discs on the Ondine and BIS labels and enjoy his music, which has led me on to listening to the likes of Vasks and Tubin. Of the symphonies, I don't think I've heard Nos.3 or 6. I tend to prefer the later ones.