Questions are asked almost daily about the Welcome Card, and generally get the correct response that you have to do your research, because there is no one answer: it depends entirely on you and what you are interested in and whether or not you're likely to make use of enough of the discounts to make it a good option *for you*.
I've always pointed out that the discounts on the entry fees to many of the attractions will be small: a euro here and a euro there may not add up to much; but that it's the discounts on more expensive activities that really do add up.
Here is an example of what I mean. I've just returned from five days in Berlin. I knew I wanted to go to two operas, Tosca at the Staatsoper and Turandot at the Deutsche Oper. The 5-day Welcome Card for zones ABC cost me 35.90 euros. The 25% discount at the Staatsoper saved 13 euros, and I saved another four euros at the Deutsches Historisches Museum - the two together, 17 euros, saved me almost half the cost of the Welcome Card, and the remaining 19 euros bought me unlimited use of the entire public transport network for five days.
Now that really is good value - and it would have been even better value had Turandot not been sold out.
All three opera companies, and all the main theatres, are partners to the Welcome Card scheme and all offer 25% discount. So if you enjoy theatre and opera, there is no question that the Welcome Card is very worthwhile. The snag is that you can't use it for online booking in advance. But you can order in advance by phone, and get the discount when you come to collect the tickets. If you've paid by card on the phone you can collect the tickets just before the performance; if you haven't paid you'll have to collect them at the theatre a couple of days earlier. I've used both methods with the Berliner Ensemble. If I'd done this for Turandot the total discounts would have saved me almost the entire cost of the card. But I naively assumed, alas, that I'd be able to get a ticket on the night, as I'd always been able to on previous occasions.Edited: 7:31 pm, October 28, 2012