I saw this film just the once, when it first came out and I was in my teens. I remember it being on a par with Cliff's other films - enjoyable, colourful, escapist nonsense, enhanced with some good songs.
But what has happened to it? The Young Ones, Summer Holiday, and Wonderful Life have all featured regularly on British TV and have had video and DVD releases, yet Finders Keepers has disappeared almost without trace (this is also true of Cliff's subsequent films Take Me High and Two A Penny, but they weren't musicals: Finders Keepers is.
The film's songs are all good. Written by the Shadows, they are mostly cheerful and plot-relevant, and they include the haunting This Day, a ballad performed while boating through subterranean caverns, I think. The soundtrack is well worth a listen.
Personally, I'd welcome an opportunity to see the darn thing again.
Addition: I have acquired a somewhat under the radar DVD of Finders Keepers - dubbed from an off-air VHS taping, I suspect. The songs are, indeed, all very good. The rest of the film, alas, is not. The plot is ludicrous, the script is poor, people behave in all sorts of illogical ways, and even the British comedy stalwarts are ill-treated by what they are given to do (I never thought I would report that John Le Mesurier wasn't very good but, sadly, it is so). And the editing of the climactic musical number is shambolic.