At the risk of appearing to fall in with some of the knee-jerk responses (just a touch of xenophobia there perhaps?) that have gone before, I have to say (having lived in Germany, not too far from where Martin is, some 14 years ago) that the idea of a German "fun run" strikes me as, well, oxymoronic. Oh dear, now I've said it.
In any case, I've never come across a "fun run" over here that didn't include a significant number of participants either trying to win or else finish as high up the field as possible. Witness the recent Hoylake 10K - yes, I was one of them!
By all means have a go Martin - it's a great distance to race over. The only thing I find slightly curious is that you can't find a "serious" 5K race in its own right over there. If I found myself living in Walldorf once more, the absence of a regular opportunity to race over that distance would rather p*ss me off.