Hello again. Our plans (2 adults, 1 13 year old) are slowly but surely falling into place. After spending 2 nights in the St. Goar area we will head down to the GP area. We have a car but not sure about driving in one day. Is this an especially scenic drive? Is there a must see town/village on the way where we might want to break up trip and spend night? TIA.
It depends on which route you take. The most direct drive goes along A3 to A7. A3 passes through some low mountain territory after Frankfurt and gives you a good view of Würzburg, but otherwise isn't too exciting. A7 roughly parallels the Romantic Road. The actual scenery from both the Autobahn route and the secondary roads that received the "Romantic" designation involve nothing particularly interesting until the Alps come into view near the southern end. Several of the towns along the way, though, are popular destinations (Rothenburg odT, Dinkelsbühl, Nördlingen, Augsburg, Landsberg am Lech, etc.).
An alternative route that takes longer but offers better scenery would be to drive along A5 south towards Karlsrühe. From just south of Darmstadt to Heidelberg, you'll see a low mountain range (the Odenwald) lined with castles, vineyards and several attractive towns (Heppenheim and Weinheim are the highlights). At Heidelberg, if you leave the Autobahn and follow the course of the Neckar river upstream, you'll pass scenery very similar to the Mittelrhein... a deep river valley with plenty of attractive towns and castles. Some of the highlights are Hirschhorn, Bad Wimpfen, Neckarsteinach, Eberbach, and of course, Heidelberg itself. After Bad Wimpfen, follow the signs to A6, and continue in the direction of Nürnberg. Along the way, Schwäbisch Hall makes a good scenic detour for an hour or so. A6 intersects with A7 just to the north of Dinkelsbühl, which might make a good overnight stop if you choose this route.