Hi Nick, welcome!
Your list of vest advantanges seems pretty complete to me.
I only hike in one in very cool weather, and then it's generally either fleece or fiberfill, not down, due to moisture management. But a down vest in camp is (IMHO) the most warmth for weight of any garment. Layered between a longsleeve shirt and a shell jacket it provides excellent core warmth while not piling on a third (or fourth) sleeve. Better quality brands made with light fabrics and good down are extremely light--just a few ounces--and pack tiny.
For the same reasons, they're great to toss into a daypack for extra warmth while taking breaks. A down vest and lightweight windbreaker make a great system.