The city pass was great so easy just hopping on and off of the trams, if you made an error you just hopped off and tried again with no worries of extra costs. Admission to the museums was great as you could often miss the long queues waiting to buy tickets and go straight in. I do not think the I amsterdam cards saved us a vast fortune as there are only so many places you can see in one day but it was worth every penny for convenience.
The Brussels card was great, with only two full days in Brussels and a long list of places to visit it saved a lot of time and money. The book that came with the card was also very helpful along with the free city map.