Here's a topic I have been thinking about. But before I cause a Ricknik-land firestorm, allow me to define "overrated". For the purposes of this posting, let's use the term to mean "not quite worthy of the absolute singular attention it receieves". Meaning, the site, city or monument is probably very enjoyable and deserving a look. But perhaps not as unique as advertised, or a place that may have any number of more accessible alternatives, depending on the individual itinerary. So, with that being said, here are my nominees.
Rothenburg ob der Tauber Quite simply, Germany is filled with towns that preserve their historical architecture very well. You usually don't have to travel very far from any one point in country to find several examples. A not insignificant number even maintain all or part of their old defensive walls. Rothenburg might be one of the larger examples, but it's far from the only one. And unfortunately, it's been absolutely consumed by the tourist trade. Rothenburg is worth seeing if you're headed in that direction anyway, and it sits conveniently between the Mittelrhein and southern Bavaria. But if you need to travel far out of your way to see it, you're missing quite a lot along the route. And I wouldn't miss nearby Dinkelsbühl or Nördlingen for Rothenburg.
The Romantic Road You will probably enjoy the scenery along this road... as you would if you drove along just about any rural road in Germany. The road itself is nothing special, but it does link together some attractive towns. Also, it's only one of about 100 officially designated Feierenstraßen, or themed holiday routes in the country, but just about the only one known in English-language countries.
Salzburg Yes, it is an attractive city, and it offers some stunning views of the Alps. But compared to several other cities in southern Bavaria and western Austria, the Altstadt, the focus for most visitors, is really small. Smaller than a large shopping mall. Even the ski resort of Kitzbühel, with an almost insignificant year-round population in comparison, has a larger Altstadt. Also, when you've seen towns like Landshut, Passau, Burghausen, and Rosenheim, you notice a certain style of architecture with particularly brightly painted facades. I first visited Salzburg a day after seeing the Technicolor brilliance of Landshut. Salzburg, although built in a similar style, seemed oddly monochromatic, with most of the buildings painted dull shades of white. I do think that Salzburg makes a good stop between Munich and Vienna, and perhaps even a base for exploring some of the Alpine sites in the environs. But as a destination in and of itself, I don't think Salzburg holds up completely on it's own.
And now the biggest heresy... The Berner Oberland. Yes, it might be one of the most beautiful locations in all of the Alps (I put it just below the Mattertal in terms of natural beauty). But the Alps almost everywhere are stunningly beautiful, and often much cheaper. True, when I have visited under good weather conditions, it has never disappointed. But I can also say that again about most of the Alps. I wouldn't miss the Berner Oberland if it's convenient on your itinerary, and at the right time of year, but there are plenty of other Alpine locales where you can also get a great mountain experience, and many of these are much more convenient to the typical Grand Tour itinerary. And many that are much cheaper, even in Switzerland.