If you would like a fun, big festival but without the hype of the Oktoberfest, then come to Frankfurt the last weekend of Aug. for the Museumufer Fest. (Museum Riverbank Fest) Both banks of the river are covered with 20 stages, artwork & craft items for sale, all kinds of international foods, myriad events taking place in all of the museums and around them too, dragon boat races, fireworks, and tons of other stuff. For the last 2 years, over 3 million people have found it worth coming to. It is now one of the premier events in Germany. Frankfurt itself is a great, historical city to visit with wonderful little gems of history scattered all through the city. This WAS the Imperial city where the elections and coronations of the Emperors took place for hundreds of years.
There is also Unification Day on 3 Oct. and there are all kinds of events planned in Berlin especially since this is the 20th anniversary of the fall of the wall. Berlin is where I would head to instead of Munich. If you want to see a castle or palace you can head over to Potsdam and see San Soucci, which is gorgeous along with the surrounding park and everything in it.