Tourist trap: Yes and No.
When I did these trips (many moons ago), the Swiss rail pass / Euro-domino was enough to board the train, so the whole could be pretty affordable for foreigners, even in First Class. Bring your own drinks, food, etc and it won't break the bank (apart from Switzerland being an expensive country for about everything).
Buy separate Glacier express tickets and it becomes expensive. Buy drinks and food on board, and you have to rob your bank.
On the other hand, it's a pretty challenging time table to do the whole stretch in 1 day on "local" non-Glacier often non-express trains. The connections, the additional stops, etc, it goes far above the "regular" 8 hours, not to forget all "worries" about making the connections, jumping platforms, different railway companies to deal with, separate reservations, arriving late at your destination, howling around your luggage and the like. Still, nice though.
Ah, and when you want to do the Glacier Express: Switzerland does have some more just as beautiful stretches, like Montreux - Interlaken, Domodossola - Locarno - Bellinzona, Lugano - Luzern, Sankt Mortiz - Tirano and several local old train stretches like Brig - Chur.
And when you are in Europe anyway, Austria does have some similar stretches like the Arlberg and Semmering.