I heard an interview with Cliff some time back where he spoke of the filming being a bit of a nightmare - it was the wrong time of year and while looking like a sunny holiday paradise it was actually quite cold (!) plus the sand 'on the beach' was covered in a black tar...!
Cliff said unlike 'Summer Holiday' it was a chore not any fun to make - besides one section of the film the 'salute to the cinema' part that saw them imitating figures off the silver screen from Charlie Chaplin to James Bond ! - Cliff said that bit was great to do but otherwise the script was quite weak and overall the film was as you say 'a bit of a muddle' !
the songs by Cliff/Shads notably 'On The Beach' and 'A Matter of Moments' plus The Shads superb 'Theme For Young Lovers' and the excellent 'Walkin' make the thing worthwhile....and young Susan Hampshire was utterly gorgeous !!
as I said script wise it's not another 'Summer Holiday' and I even like 'Finders Keepers' better as an overall film, but that said The Shads are well featured and Cliff and the gang are always enjoyable to watch re the nostalgia angle