Looking at a 7day itinerary and ending in Budapest for River cruise, is the Golden Pass from Zermatt to St Moritz a must do or is time better spent in the Junfrau Region.
Is the Golden Pass worth it?
It is actually the called the Glacier Express. Worth it? De gustibus non disputandum est. I guess if people didn't like it, they wouldn't run 3 trains a day each direction during the summer. It is a very scenic 7 hour train ride on a nice day.
The rail route from Zermatt to St Moritz IS NOT the Golden Pass route, it is the route of the Glacier Express.
The Golden Pass route is Montreux - Interlaken - Luzern.
All these named trains (Glacier Express, Golden Pass, Bernina Express) are just extra trains for tourists with restaurants etc. You can travel the same route (or any other rail route in Switzerland) by the regular hourly trains, and you see the same mountains out of the window.
The route from Zermatt to St Moritz takes most of a day. If you can incorporate this route into your tour of Switzerland do so, it is very scenic. But do not go all the way across Switzerland just to come back again.
Here is a rail map of Switzerland which may help. All the red lines are rail routes, all of which have at least one train per hour: https://www.sbb.ch/content/dam/infrastruktur/trafimage/karten/karte-sts-pass-gueltigkeit.pdf
You can look up train times on the SBB (Swiss Federal Railways) website: https://www.sbb.ch/en/
I would rate the Berner Oberland where Jungfrau is located higher than the area of St. Moritz.