Is zakat due on a luxurious dwelling if its value has greatly exceeded its purchase price, or is zakat absolutely not due on a dwelling, no matter how high its value?

There is no Zakat on real estate if it is not intended for sale and trade. Therefore, a house is not subject to Zakat, even if its value is high, because it is not intended for sale. It cannot be analogized to jewelry, because the original ruling for jewelry is the obligation of Zakat, but it is exempted from this original ruling due to permissible use.