Interesting. What seems to be emerging is that

- 32 bars, or 2x16 bars, is a good length for a structured dance
-- although 2x32 is fine for 'last waltz' type dances, or for playing without dancers

- you can get to 32 by playing a 2x8-bar tune AABB, or by playing a 2x16-bar tune straight through

- a lot of 2x16-bar tunes have built-in repeats, so that when you play them straight through you are effectively playing 8-bar sections, AABB or AABA

Then (getting away from waltzes) there are tunes like Speed the Plough which repeat in 4-bar sections with small variations, so AABB is more like AAAABBBB, and tunes like Black Joke which have a 4-bar A and 8-bar B - and presumably should be played AAB or AAAABB... and on it goes. Fascinating stuff