There was a discussion on 18D in answerbank "crosswords" page 7 at 10am today. Elsewhere "wayside" music is described as experimental/progressive rock .. not middle of the road - I'm more swinging sixties!
Thanks Julie, just looked at 'crosswords answerbank' (for anyone else that's interested this is one of the explanations): SWAY (rock) + IDE (i'd say) = Wayside -garage music. I'm more the Sixties too and have never heard of garage music!
I think the music references are red herrings.
Rock I'd say = anagram of i'd say
case of "garage" - best i can do here is - garage/warehouse - 1st and last letter of warehouse.
is not middle of the road = side of road