sticking more or less to your proposed route I would make the following changes:
From Merano go take the road to Vipiteno/Sterzing via San Leonardo, which crosses the Jaufen Pass. Then go south and take the Penser Joch Pass to Sarentino and Bolzano, where you carry on along your planned route.
From Leipzig don't go staight to Magdeburg, but instead go via the Harz mountains. Great sights there are Quedlinburg, Goslar and of course the highest point, the "Brocken". From there instead of returning to Hannover, travelling along the small roads along the Elbe river is more rewarding.
My 2 cents worth
Only when we pause to wonder
do we go beyond the limits of our little lives.