This is the simple grammar “A は B だ” meaning “A is B”. は is the particle which indicates the topic of the sentence and だ is attached to a noun or na-adjective to make the statement declarative.
貧乳 means “flat chest”. The kanji literally means “poor breast”.
ステータス means “status” or “status symbol“. It’s usually used for something valuable such as a watch, car, credit card, occupation and so on, which shows a person’s social status. So she is saying “having a flat chest is one of the valuable things in society”.
This time the topic is omitted as it’s clear that she is still talking about “a flat chest”.
希少価値 means “precious rarity” or “rarity value”. The kanji 希 means “rare”, 少 means “few” and 価値 means “value”. So it’s used for something that rarely exists which makes it more valuable.