I don't think the term is suspect at all. The concept of Grossdeutschland had existed at that point by approximately 175 years, and was discussed frequently by a Nazi-predecessor party, the Pan-German League, in the 1890's.
Hitler referred to Grossdeutschland throughout his early works, but most especially after his "Heim ins Reich" initiative, which immediately preceded the Anschluss and the violent dismemberment of Austro-fascism (because they were considered to be traitors to the concept of Grossdeutschland).
Grossdeutschland was not made an official title for HItler's "empire" until 1943, which may be where the confusion is coming from. It was definitely used prior to 1941, however, in German propaganda. As such, I would consider this piece Nazi "propaganda", rather than an official representation of the German State.
That being said, after writing the above spiel, I've found your medal (see the very bottom of the page on the following links):
http://www.historama.com/online-history-shop/israeli_zionist_judaic_exonumia/anti-semitic_medals_jetons_tokens.html
http://legacy.stacks.com/Lot/ItemDetail/62578
http://www.mcsearch.info/record.html?id=258621&tab=4
http://www.od43.com/Anti-Semitic_Plaque_Pi.html
Of course, Google Books has the book referenced in some of these links, Bruno Kirschner's "Deutsche Spottmedaillen auf Juden" from 1968, through which you can get a sneak peak at your medal's info by searching for "1939":
http://books.google.com/books?id=_AEJAQAAIAAJ&q=1939#search_anchor
I still haven't found any authoritative source on the price, but apparently some websites think this thing is worth $600 to $800. Who knows if those prices (or the medal) are for real, but if they are, this seems like a really neat (albeit tacky) piece of history to own.
I would suggest getting your hands on the Kirschner book before laying out a ton of money for this -- I believe it is real, if a scholar back in 1968 published a book identifying it as a legitimate medal. I'm led to believe Kirschner is a reputable source as it is published by Ernst Battenberg Verlag, which is the same outfit that published the Grosser Deutscher Munzkatalog. Additionally, though, I'm sure this is something there could be tons of fakes of out there, so that's something to watch out for too.
As a side-note, I disagree with the translations many of these people are going with. The obverse translation is straight-forward, but I think the reverse translation is directly referential of both the obverse legend as well as the items (money, bombs, etc.) depicted on the reverse. Therefore I stick by my original translation.