It's funny you should mention this. I was listening to it yesterday and had the same thoughts.
I think it was very influential. I too was a Rock guy when I first heard this in the mid-seventies. I had never heard most of the artists and songs on it. I came to love it. I have since bought CD's by many of the artists on it.
I think many, many people were introduced to Bluegrass and Old Timey Music by this album. I also enjoyed WTCBU II, especially Bruce Hornsby's Bluegrass rendition of his hit "Valley Road".