Although your parallels are interesting, I fail to be convinced. It's great to see parallels, and very tempting to spot more and more, but it can sometimes become a case of seeing parallels everywhere. Some that you cite could happen in any two books, or are merely similarities due to the characters and situations.
For example - the overseas plane trip - this would be a natural thing, as the children's parents are aviators, and also because Prince Paul has an aeroplane.
Landing on a plain - pretty obvious place to land - it's not likely they would choose to land anywhere more tricky.
Meeting a youth half naked and barefooted. Again - they need a 'guide' to the local terrain - and as they are 'creatures of nature' both characters are likely to be barefooted. There is also a nod to folklore and legend - they are very much traditional native people. Enid had poorer characters going barefoot in many, many books. It was something she regularly did, so the coincidence or parallel isn't particularly striking.
It would also be quite natural for the children to want their new native friend to come and live with them afterwards, but Enid realised this would not be practical, in case she wrote other stories and had to include them, as well as for the cultural reasons.
The baddies disarming the newcomers of their guns is a pretty sensible move on the part of the baddies - again, something I see as being essential to the capture of the goodies. If they didn't disarm them, the plot would have been quite short lived!
Rivers and waterfalls have played large parts in many, many Blyton books. Quite how this can be seen as a parallel I don't know - River of adventure, a river in The Rockingdown Mystery, rivers in many Famous Five books, underground rivers in several books. Waterfalls are great places to hide, have secret tunnels behind, and are spectacular additions to a story to give a sense of place because they conjure up sight and sound for the reader.
The extreme fear of the bad guys by the native guides is also something that happens in a few books -the guide David in Mountain of Adventure is a good example. It's a natural device to create tension in the reader if someone is terrified of an unknown enemy, then the reader will feel a sense of foreboding.
A flyover of the mountain and forest when going home - again - that's going to happen, given the settings. Enid often looked at her setting from on high, or far away, at the end of a book - she did it in several of the Adventure books, and even in books like Mr Galliano's Circus and The Six Bad Boys. This is what I describe as being 'filmic' - the last shot before the film fades out.
The tunnels in the mountain - a device used many times in various books - too many to list.
Obviously when climbing rough terrain the characters need places to rest and eat and hide - these things can hardly be said to be a parallel except in an obvious way - rather like saying 'all Enid's holiday adventures contained picnics.'
I could go on - but I won't. I don't mean to pour cold water on your parallels - these observations are always interesting and fun to speculate on, but often one person sees special significance in things where others might not. I certainly don't think Enid was the type to consciously include all these parallels. If they are there, they are there because she often used them, and it just so happens she used them in two consecutive books in the same series.
I've enjoyed reading your theories though - I can see you've taken a lot of thought and time to draw them up and it's always good to speculate.