I agree with your view on chickweed it is the best rearing food you can give to your birds and love your sentiment regarding it in your post.
As a rearing food I give my birds a mix of eggfood,grated broccoli,grated carrot sprouted seed with a spoonful of honey and a dash of powder multi vits.
Chickweed,groundsel,Sheppard's purse,plantain,sow thistle and knot grass are all coming into season now and are a great rearing food as well...