That is EXACTLY the type of dress I'm looking for: moves like a dream, weighs nothing, and looks gorgeous. But I don't know enough to say "ok, use the bodice from dress A, but use the skirt from dress B, and remove the underskirt, and don't use any boning at the hem" (since I don't even know what all of that means).
The bodice is the neck-to-hips section. You can choose whatever design you want.
Not all gowns have underskirts, but those that do have a poofy/flippy look to the bottom, and there's an inverted cone thing going on in the silhouette of the skirt. 99.9% of the time, those gowns are worn for International Standard, rather than American Smooth. (the other .1% of the time, someone is wearing a Standard gown in Smooth.)
I think of the skirt you see as Skirt, usually made of a soft, lightweight fabric. Underneath Skirt is Underskirt, usually made of a stiffer, but still lightweight, fabric, with a ruffle or something with huge circumference toward the hem. Both Skirt and Underskirt are finished with Soft Boning/horsehair braid, which is a flat, flexible, ripple-y nylon thing like stretchy, loose-woven tape. Underskirt's ruffle and all that ripple-y soft boning make the hem of Skirt move a lot if all you do is blow on it, never mind do a double reverse spin at speed in Quickstep (you'll understand one day, dear).
The green, maroon, and blue gowns have underskirts; the green underskirt is a different shade of green; maroon gown had a black underskirt; blue gown has a paler blue underskirt. Underskirts show when you're moving along at a reasonable clip, so the color shows, and is a fashion choice. Like so:
The red gown has neither soft boning at the hem, nor an underskirt; it is a Smooth gown. The skirt hangs fairly straight, and doesn't whip out until I make it move. This encourages me to make it move...
goodness, my legs are... solid
I couldn't help but notice that all your choices follow almost the exact same style, which happens to be my preferred style as well: either V-neck or rounded neckline with stoning in a V shape; stoning on the bodice but very little on the skirt; another wider V shape just below the waist (except on the red one, which is just as pretty); long sleeves but bare shoulders; full circle skirt with no godets; open back but not cut too low (which means a more supportive bra can be sewn in). And I love all your vivid colors!
I have a useful decollete; might as well use it, so wide V/portrait necklines and bare shoulders. I have heavy arms; sleeves. I have a "spare tire" so I do not wear gowns that are fitted to the hips; might as well dress as the Michelin man. So: full-circle skirts, starting above the hipline, if possible. I am no kid, so no low back for me.
Oh, and hey - if you are "mildly horrified" that you have too many dresses, I'd be delighted to help you out and take one off your hands...how tall are you, exactly? After all, I'm in the market for a smooth dress....
Alas, I am at least six inches shorter than you. But you can get your own made for a Very Reasonable Price, and I encourage you to do that. FWIW, the dress changes EVERYTHING. How you stand. How you walk. How you present yourself. How you dance. Get a new one. And get copious advice before you order it, from people you trust. It cuts down on unpleasant surprises.