As the others have already mentioned, it was prepared for and flown on the return flight of the first Germany to USA flight of the Graf Zeppelin. Like every Zeppelin flight cover as well as every first flight cover of any kind it is significant. Though, if by asking if it is significant does that mean rare and valuable then perhaps not so much. There was so much news hype about this flight at the time that a great deal of mail was prepared and flown on it and most of it was saved by collectors. There are several factors that go into the present commercial value of the mail including whether it is franked with the correct airmail stamps of the day which is a plus and if not, such as yours, that is a minus. Next is whether it was cancelled at Lakehurst, New Jersey where the Graf Zeppelin was and left from which is a plus or if it was postmarked in some other city such as yours which is a minus. Next is whether there is an appropriate supplemental cachet in addition to the one shown on your cover which was applied to every cover which is a plus or there is nothing beyond the standard cachet such as yours has which is a minus. Clarity of both the postmarks and the standard Zeppelin flight cachet are also important and yours are not perfect but they are very good so yours would be somewhere in the middle. And of course overall condition, neatness and attractiveness, and whether there is any damage will factor heavily. As for whether this was ordinary commercial mail that happened to get put on this flight I am not sure I would agree that it is ordinary commercial mail. Pretty much all mail that was flown on Zeppelins, at least until the regular flights of the mid-1930s, was philatelic in nature. Covers from this particular first flight sell on
ebay pretty much every week and they go from about $15 to as high as $35 unless there is something particularly desirable about them such as being signed by the Zeppelin's captain and crew or if they have one of A.C. Roessler's forgery Zeppelin overprint stamps on them. My guess is that yours might go for somewhere in the $20 to maybe $25 range if you put it up on
ebay, though it could go for a few dollars less or more.
There are a great many hundreds of different first flights of the Zeppelins that were made between 1909 and 1939 and there is an excellent catalog on them all - the Sieger Zeppelin Post Katalog which has been out for a very long time and is now up to its 22nd Edition.