You have a great occasionwear capsule, Sal! Can't show you pictures of mine, as I am recovering from some surgery yesterday and still feel rather dizzy, but I can tell you about it's content and how I use it.
Party dresses have always been difficult for me. Most seem to have a deep decolletage and/or have other lines that don't harmonize with my figure and/or are in fabrics that feel unnatural to me. Well, I just received as a gift a beautiful long-sleeved grey-blue Italian dress in silk chiffon and lace that (sensationally!) fit perfectly. But generally, my party outfits are two-or three-pieces, which have plenty mix-and-match potential, so I can vary my outfits according to the occasion, season, and my mood.
Through the years, I have collected six midi or ankle-length skirts that I use as partywear only, because of the fabrics, which are too elegant for my everyday activities. (Colours: two shades of pink, a print in navy and silver, light turquoise quilted with metal threads, silvery taupe, and black.) Plus one simple sleeveless black&silver lurex midi dress. These items are stored in a separate hanging cabinet in my attic, together with some tops (sleeveless, short sleeves and long sleeves), toppers and scarves/shawls. However, some of these tops and toppers will also be used as part of my regular spring and summer wardrobe. On the other hand, a self-patterned silver wrap skirt from my summer wardrobe, some spring and fall dresses and a couple of long-sleeved lace shirts/blouses from my regular spring and fall wardrobe will also be considered as partywear in winter (and will then be placed in the "party" cabinet). So you see, my capsule is rather flexible.
At present, I have only one pair of shoes that I view as "party shoes only"--tall block-heeled silver pumps. And I am not on the outlook for more. In many cases, I will use ballet flats, pumps, nice sandals or sleek boots from my regular wardrobe.
I agree with others that there might be few occasions for formal wear. However, I personally enjoy dressing up a bit when possible. I love an relaxed elegant style, so I often mix items from my party wardrobe with those from my regular wardrobe. Examples: an elegant ankle-length skirt worn with a turtleneck pullover and sleek boots; a bold silk blouse worn with black jeans and silver pumps; a velvet or shimmery wrap/shawl worn with a simple knitted dress.