These characters combine literally to mean “a treasure of no price” or “without-price's-treasure.” The structure itself elegantly communicates the idea that the item's value cannot be measured in currency.
In Chinese culture, there is a strong emphasis on value that exists outside of the material and commercial spheres. 无价之宝 is a linguistic embodiment of this value system. While a new car or a luxury watch might be described as `很贵 (hěn guì)` (very expensive), they would rarely be called a `无价之宝`. This term is reserved for things with profound significance. This concept can be contrasted with the Western idea of “priceless” as often used in marketing (e.g., the Mastercard “Priceless” campaign). In American culture, “priceless” can describe a funny, ephemeral moment. In Chinese culture, 无价之宝 carries more weight and permanence. It often connects to core cultural values like:
无价之宝 is a formal and heartfelt term. It's used to express deep appreciation and place a high, non-material value on something.
Its connotation is overwhelmingly positive and sincere. Using it lightly or sarcastically would sound very strange.