It is a nice art deco cover. In fact, the cachet on the front of that cover is one of the earlier works attributed to Leo August, who later with his brother co-founded the Washington Press and the Artcraft line of covers.
Per my 2013 Scott Specialized, the catalog value of the cover is $40, however one just like it was recently sold on
ebay for $9.48, which is a little under 24% of catalog value, and is probably indicative of real world prices. See link below:
http://www.ebay.com/itm/Scott-735-B...em4d1f5ae492Also note that the Souvenir Sheet of 6 on cover is considered a Scott 735 (not 735a, as that suffix letter denotes a single stamp).