Munich to Berlin then Belgium

I agree that moving Frankfurt to after Berlin makes sense. As a break from all these European cities and their cathedrals, maybe treat the hubs to a rental car for a few days to explore the Mosel Valley (in addition to the Rhine), where there are lots of castles, including the very popular Burg Eltz. I liked Landshut, which is near Bernkastel Kues. It's mostly ruined and mostly free to visit and has great views over the valley. Others on the forum recommend Marksburg. The scenery in Mosel is top notch. Look at staying in Zell or Traben-Trarbach, rather than Cochem. Even better is tiny Enkirch, which has a small hotel that looks quite nice.
A quick google search suggests the Bundesliga (German football) would still be going at the start of your trip. Watching a match in a beer garden would be fun for a sports fan.

Looks like a lot of backtracking. I recommend starting in Budapest and working your way North to Berlin, the Frankfurt and finally Belgium.

If you are interested in history and / or art I recommend spending more time in Berlin - normally 4-5 nights.

We're flying into Munich and must be in Berlin for a concert on day 15

These two requirments sound set in stone. So, my suggestion is to do Frankfurt/Rhine immediately after Munich. Then fly to Budapest. If there is a night train that works Frankfurt to Budapest, then that may be better. The continue on to Prague and Berlin.

alternative locations that I should consider?

Yes. You pass through Vienna on your way to Prague from Budapest. I know there will be some who disagree with me on this, but I recomment dropping one day from both Budapest and Prague and adding two in Vienna.

I am with jkh, I love Vienna and if it works out, stop off there. Also, if you have a day to add to somewhere, add it to Munich. For some reason lots of forum members seem to spurn Munich. We spent 6 days there and never got bored. It's a great city! Would you be able to fit some time on the Romantic Road (Dinkelsbuhl, Rothenburg, etc.)?
Have fun planning and travelling!

@Judy- I too loved Munich and you could do worse than spend another day there. Lots to do in and around the city, museums, walking tours or even just hang out in the Park.

• Day 1 Munich (fly in this day)
• Day 2 Munich
• Day 3 Munich
• Day 4 Munich / sleeper train

I suppose you have planned what interests you in Munich and it takes 3.5 days? Otherwise I would take that sleeper train a night earlier. But to be fair, I have never been to Munich, never been able to build up interest despite a lot of reading. If you have a love for going there, great, otherwise fly into Vienna instead of Munich. For me Vienna is worth the see for 2.5 or 3.5 days and I say that not being a great Vienna fan.

Then there is the issue that you are arriving in Budapest too early to check in and tired because few sleep well on sleeper trains. Might as well call day 5 in Budapest a half day for all practical purposes.

• Day 5 Budapest
• Day 6 Budapest
• Day 7 Budapest
• Day 8 Budapest / sleeper train

Again the sleeper train. Okay, with all of the jockeying around to store and retrieve luggage and getting to the train station you might as well call day 8 a half day. So you have 2 full days and 2 half days in Budapest. I think you are a full day short of a good trip …. But you wouldn’t get bored in 5 full days (but I am biased of course).

• Day 9 Prague
• Day 10 Prague
• Day 11 Prague

I would only count day 9 as a half day for the same reasons above. So you have 2.5 days in Prague. Not ideal, not terrible either.

• Day 12 Frankfurt / all day train
  

I would fly in the morning and spend more time on your trip to Berlin. Not even stay in Frankfurt, hit the road when you land.

• Day 13 Frankfurt / Rhine Valley day trip

Apparently the Rhine Valley day trip is important to you. Otherwise no reason to go to Frankfurt. Among the places I have been in Germany (not many to be honest) it was the least “impactful”. But I suspect you have some sort of driving trip to Berlin arranged and that could be interesting. If you skip this and fly from Prague to Berlin (or train), then put a day in Budapest and a day in Vienna. Use the time for day trips out of each city. See more and pack and unpack less.

• Day 14 Berlin
• Day 15 Berlin (must be in Berlin this day)
• Day 16 Berlin
• Day 17 Berlin / sleeper train to Brussels

I would drop several days from Budapest and spend them in Vienna. I would also think about a way to spend a bit less time in Munich. To each their own, but to me, this trip looks like it will be skipping past a lot of good places to only highlight a few major attractions.

Its hard to decide to return to a place that you realize after the fact that you should have spent more time in, but much easier to go to a new place. For me its a difficult compromise between seeing Central Europe and seeing Germany. Maybe if German is calling you forget Prague and Budapest and do Germany well. Or if Prague and Budapest are calling then you forget about Frankfurt and the Rhine valley and Munich and concentrate on Budapest, Vienna, Prague. Berlin is a stop that works with either scenario so that doesnt change.

You may be happy with just the cities. But if you narrow down the region you are visiting you can see more of the places inbetween and do a few over night trips from a base in a large city. There are a lot of options for every place you have listed. I can only describe the one place I know enough about to sound somewhat intelligent; Budapest.

Vienna to Budapest with stops in Pannonhalma (archabbey and Gyor (old town), Day trip out of Budapest to Szentendre and Esztergom and Etyek. Overnight trip to Eger and the surrounding wine country .... or an overnight or two night small winery tour ... or Lillafüred for the forest train, nature, caves, hot spirings ..... .

And like i said, from Vienna and Prague the same sorts of things are possible.