Youre pretty opinionated! All these people suggesting Dresden but you do not want to include it.

Another vote from Dresden ... but enough about that.

You say they are doing this without car? Yikes...for me, too many stops and transfers for parents to manuever with suitcases. It sounds like more of a back-backing itinerary. I'm 50 and too old to rough it. I vote for a rental car.

I love MUC and Bavaria ... but any mention of Oktoberfest and I avoid the entire region. IMHO, the worst time to visit. (One of the previous posts mentions travel in October ... you do know that Oktoberfest is starts 9/21 and goes thru 10/6)

Another vote to avoid FRA. Nothing to do in FRA. It is an industrial/banking center. So many Americans believe, because it is their port of entry to Europe, that is should be on the "must-see" list, but nada! I only stay at the Sheraton FRA the night before a flight to an very-early wake-up call.

I like your idea of staying in Mainz. Lots of day trips in the area. If the weather is nice, I have suggested to several friends they take a K/D boat from the Mainz Wharf to Cologne ... beautiful scenery, castles, vineyards, etc. Get off in Cologne, stroll around, take the train back to Mainz.

I think the interior of Newschwanstein is worth it. However, during Oktoberfest: see previous paragraph.

When in Rothenburg, I either stay at Eisenhut or (as in many small towns) a B&B.