That episode in question I think was supposed to be something more ambitious, but due to budgetary problems, they couldn't produce what they wanted, hence the recapped footage. It's also the tail end of what I think is the lowest point of Nadia: the Africa sequence. There I felt all the characterizations were totally destroyed, and the animation and the dialogue were worse. Not only that, but the newer characters introduced were not even remotely INTERESTING; Grandis' ex-fiance was especially bad. Plus, considering that Nadia had admitted that Jean was more important to her than the Blue Water, and hey, rushed into his arms nude, you know that her sudden 180 turn in the subsequent episodes feels very out of place and doesn't make a whole lot of sense. (Not to mention totally out of character--the Island episodes were guilty of messing with her personality and relationships with her friends, but it is far, far worse.) Even for a character at odds with her own views of the world, it just didn't fit. Again, episode 35 disregards this substory and acts like it never existed.
All in all, NADIA is indeed a fine show, but it's too bad that it suffers from such a terrible filler arc. Even Hideaki Anno admitted to being dissastified with the final result. As a matter of fact, the closest to a streamlined version of NADIA that he came to was with "The Nautilus Story", where the island/Africa episodes are all but omitted save ep. 31, and the story concentrates more on the struggle between Nemo and Gargoyle. Pity that version's only available in Japan.