I found 'Treasure of Matecumbe' just about entertaining, helped by the impressive main cast.

Peter Ustinov, after a poor showing in 1975's 'One of Our Dinosaurs Is Missing', comes back strong with a top performance as Snodgrass. Joan Hackett is also enjoyable as Paxton, especially across the first act. Robert Foxworth fits in too, as he plays Uncle Jim. The two kid actors are Johnny Doran (Davie) and Billy Atmore (Thad), they aren't amazing but are at least likeable and are passable in what they give.

The plot is where it becomes less interesting. The adventure elements... read the rest.