We lived and worked in the area around Stuttgart, we even considered moving our boat there as we live only 2 hrs drive away. That was untill we found out that boats over 12mtrs are not catered for on the Necker. Only if you are a commercial boat delivering or collecting goods are there any moorings available. I do not suppose you would want to stop there. I will see what we can find here, information wise and let you know by PM.
I'm hunting around for printed guides to the Neckar. There's some basic data in the Rhine JPM guide and Tom Sommers paperback "Cruising the Canals and Rivers of Germany" but it would be handy to have something closer in format to the Editions du Breil series if such exists.
I would also appreciate hook-up with anyone who has close knowledge of cruising the Neckar - we'll need a crew in 2-3 years' time!