You're going somewhat backwards here. Strasbourg and Freiburg are on the way from Mürren to the Mittelrhein. It's about as easy to get from the Mittelrhein to Füssen as it is from Freiburg, so there's no need to backtrack south along the Rhine.
Nobody would ever mention Reutte if Mr. Steves didn't make it one of the more puzzling recommendations in his book. It's a very ordinary, not particularly attractive town in a region chocked with extra-ordinary towns.
If you wanted to include some geology-related sites, large parts of the territory of Rheinland-Pfalz west of the Rhine river constitute the Vulkanland Eifel Geopark. The actual sites and exhibits are spread across a rather large geographic area.
For paleontology, look up Grube Messel, near Darmstadt (very close to Frankfurt's airport). There's a nice museum devoted to all the fossils discovered in the nearby mining pits.
Evidence of "WWII history" in Germany is actually rather scant. Much of the building projects of the NS era were destroyed during or immediately after the war. Of the destinations you listed, the only structure I can think of that has a close link to the NS era is the Heidelberger Thingstätte. The Nazi government intended this outdoor amphitheater as a place to hold political rallies, although these proved less popular than the regime intended. With the exception of the removal of all Nazi-related insignia, it remains completely undamaged today. If you want to visit, you can reach it either by hiking up the mountain from the well-known Philosophenweg, or drive up to a parking lot just below the structure (the route is tricky to find if you don't know the area, however).
Another NS site that is somewhat convenient to your tour is the Olympic Stadium in Garmisch-Partenkirchen. It's still in use for skiing events. And if you want your choice of good Alpine hikes, this would be a much better location to stay than either Füssen or Reutte.
