juliette,
I took the Salt Mine tour in Hallstatt when I was there in May, and really enjoyed it! I also visited Berchtesgaden a few days prior, but didn't tour the Mine there as I figured one Salt Mine would be adequate. It's an important look at the history of the area, and I found it quite interesting to see the 'background' of such a commonly used material.
The Guide for my tour spoke German to begin with, but she was also using Italian for some of the guests (the language abilities of Europeans never fails to amaze me!). She knew there were some English speakers in the group, so used English for the most part. According to Rick's book "the Guide is required to speak English if you ask - so ask". As I can function to some extent in Italian, I was also enjoying that - it was good practise!
As someone else mentioned, another benefit of the Hallstatt tour is the view. There's a large Castle (Rudolphsturm) at the top of the Funicular, and the view from the restaurant patio there is incredible! Definitely a great place to stop for a pint (or glass of wine) and a meal if the sun is shining!
Incidentally, I'm in the mid '50s age group and I enjoyed the tour, if that's any indication. It wasn't "flashy" but I found it interesting.
Happy travels!