IIRC they had a change of style round about "Fox on the Run" single which was to my mind a much more subtle single after the full on attacks of "Ballroom Blitz" & "Blockbuster". Another later single that felt more mature was "Love is Like Oxygen".
Did feel they were capable of developing into something more but it didn't quite happen, probably a lot to do with Brian Connolly's health issues.
Sad news.