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 are decent, but it does plod along at a number of moments. It doesn't really feel like a treasure hunt until the last knockings, which is disappointing - especially given the onscreen talent. Parts of it also haven't aged gracefully, while the vibe of the film changes from serious to fun too often; e.g. you have a KKK scene, but also a runaway bride bit.
With all that noted, it is still a film I can say is good enough and one of Disney's better live-action releases from the 1970s.
I haven't seen this film for over 40 years and it has held up remarkably well. It's a simple tale of a pair of elderly spinsters who face losing their family home. Their only lifeline may come from a tale of buried US Civil War gold. Others have heard about this treasure too, so when two young boys (Johnny Duran & Pop Atmore) set off with the map in search of it, they are closely pursued by a sinister gang led by "Spangler" (Vic Morrow). They start on the riverboat where they meet the savvy Joan Hackett - who can out sharp the card-sharps; then they alight on the avuncular Peter Ustinov ("Ewing T. Snodgrass") who runs a dodgy medicine wagon and we have some fun adventures - his "Spoojoo Juice" seems as effective as an high explosive as it is as a cure for gout! Finally they rescue "Uncle Jim" (Robert Foxworth) and our intrepid team is now ready to face allcomers on their treasure trail. There is no jeopardy about any of this, the ending is pretty much written on the first page - but Ustinov is on good form and we have loads of shoot 'em ups; an explosive encounter with the KKK and even a barn-dance with fisticuffs. It does tend to limp along a bit at times, the greenscreen scenes are very basic (especially on the river) - and at just shy of two hours is half an hour too long. That said, it is a fun Disney action adventure that probably wouldn't be of much interest to kids now, but would have been in 1976.