I don't like 'Downtown', and I find Petula Clarke's voice too whiney and nasal, but what the song has going for it is that it would probably sound just as good/bad sung by anyone else.
There are some songs that I only want to hear sung by a particular singer. For me, 'The First Time Ever I saw his/her Face' has to be Roberta Flack. 'What is Life' must be Kathleen Ferrier (a recording, obviously), and I don't ever want to hear 'Lilac Wine' by anyone other than Jeff Buckley.