This Ascension stamp (Scott #77) is the second most valuable stamp in the set and also has the second highest denomination in the set. This follows a great rule of thumb - stamp collecting values are generally higher for the highest denominated stamps. Especially for older stamps where high-denomination stamps were produced in greatly reduced numbers.
This is the middle stamp of a set of US Stamps issued to commemorate the flight of the Graf Zeppelin. This is part of the iconic set of Airmail Zeppelins which were issued at the onset of the Great Depression and were quickly out of the price range of most Americans. This led to most Zeppelin stamps remaining unsold and eventually destroyed by the Post Office. Today, the Brown $1.30 Graf Zeppelin stamp (Scott #C14) is relatively scarce and highly collectible.