I don't have a BahnCard, just looking at the site I'm really not sure I'd use it enough to justify it. Booked a couple of months in advance, and compared flight prices on that day to the train. Flights were significantly cheaper.

The test offer can be pretty useful:

https://www.bahn.de/p/view/bahncard/ueberblick/probebahncard...

(It's important to cancel immediately though.)

That isn't very useful if you're a tourist who's only going to use the card once or twice a year.