The only info known about it is that wasn't made after 1990-1991 - which isn't helpful as the GDR stopped existing by then. It is an A grade instrument, as other, lower grades were sold within the iron curtain.
Musima went bankrupt in 2004. It was composed of 2 companies - VEB Music Instrument Making and Mark New Churches (I kid you not - it's a place name) is still in existence. The 'ma' in Musima and Migma stands for 'Mark New Churches'.
MNC still sell 'spanish guitars' under the Migma label and an English site can be found at
http://www.migma-eg.de/en/index2.html
There has been a continuous thread of government and private ownership of the company since inception and they may have early records of their output.
I strongly suggest that you email them with as much info as you can get from the label, any stamps or numbers etc and wait for a reply.
Let us know if you have any success.
As for its value, I would put it in the US $300 - $800 range depending on its tone and playability. It was made with the finest woods available (German spruce). I wouldn't think that the electric pickup is too much of a selling point. If original, then it's probably poor quality and could be replaced by the buyer easily enough. The Migma/Musima East European grade of instruments bring in $100 + even for a ratty example. Probably best to sell it in Europe or to a collector.
There is a German only forum that you can ask typical values at
http://www.museum-markneukirchen.de/forum/
Find a German friend.....
This is where your guitar was made in Wolhausen.