Hi! I've always shyed away from the camera, and a hand shot is probably the extent of my photos.

But I would be happy to share ideas...
To me, a long necklace (not a long pendant) is a super versatile piece of jewelry. You can wear a long necklace such as a 20 motif everywhere. I work in corporate, so when I was flying, I was wearing business suits to meet with clients. Off hours, I am the complete opposite of my stiff suit look. I dress super casual, think round neck top, skinny jeans, and Chanel ballets flat. For summer, round neck tops, skinny white Bermuda shorts, and Chanel espadrilles. Very very casual.
I am short and small boned, 5' 2", and 108 lbs. All my friends are amazons compared to me. I have a friend that is 5' 10" and one that is near 6' tall.

I am not model tall, but I am of the mind that small petite women look great in bold jewelry. They almost need it as it pops and makes a presence. Dainty jewelry does not do it for me.
A long necklace works with everything... you can wear it with a round neck, vneck, collared shirt, turtleneck, long flowing tunic, t-shirt, belted top. I cannot say the same about a short necklace or pendant. Short necklaces or pendants look beautiful against bare skin (e.g. think vneck or open collar). But to me, they compete and look sloppy/messy with round/scoop/ballet necklines.
For you, since we are on the VCA forum here, I think you are asking about the 20 motif as I am wearing one in my first photo (good eye!). You can see how casual I wear it. My top is a striped top. I was also wearing skinny jeans and red Chanel ballet flats (my wanna be French look

). Very casual. What you don't see is I am also wearing my matching Alhambra MOP earrings and bracelet with the 20 motif.
One other comment I want to add, high price does not mean formal wear. It is the design that dictates formality. A 20 motif is nothing more than a quatrefoil/four leaf clover station necklace at it's purest. A Frivole ring is nothing more than a diamond flower ring. Station necklaces and flower rings can be found in all price points, including costume jewelry. These are simple classic designs and can be worn casual.
That's just my point of view, and I hope it was helpful. If you are considering a 20 motif, I would highly recommend it. It is a very wearable piece.