Do not waste your time in Nuremberg after having visited Prague. Yes, it has an old town center which was heavily bombed during WWII and the old castle is looking good from the outside (you cannot visit the inside). Duerer lived there so it was a pretty flourishing place at that time.
On the way to Belgium (from Prague) you can stop by in Wurzburg and visit the castle. It is a wine region and it is Asparagus season which grows in the neighborhood!!!
Cologne is another recommendation to visit the famous cathedral. Aachen is quite some history, too (worthwhile doing some research). And the ring is on your way!
Have a coffee at the Meilenwerk
http://www.remise.de/Classic-Remise-Duesseldorf-english-summary.php in Duesseldorf to watch old cars.
Check out the UNESCO world heritages which are on your way between Prague and Belgium.
Stuttgart with its Porsche Museum is a detour but it also hosts the Mercedes museum...
Have fun and enjoy!