Would you recommend purchasing the Stockholm card? I keeping going back and forth.
I think you need to have a general idea of what you plan to do when you are in Stockholm. I was in Stockholm for 4 days. I did not buy one. I did not use the tunnelbana as I'm a big walker. Used the trolley once. The only museum that I went to was Skansen. So i didn't come close to being worth the money. If you are a big museum person, then it might be beneficial. On the other hand I was there with beautiful weather in May/June. If the weather is poor, then you might benefit from it. I know there are people that swear by them. So, you need to figure out what you want to do and add up the fees to help you decide.
We knew that we would be going on 2 harbor tours which were about 500 SEK by themselves. When we added the various museums, palaces, etc that we wanted to also see, it made sense to get the 3 day Stockholm pass. Having the unlimited HOHO bus and boats made it easier getting around town. We crammed a lot into our days and probably saved around 150-200 SEK each, which at the time was in the range of $20 each. Not a huge savings, but enough that we felt positive about it. People who don't want to try to max out their usage will probably get marginal or negative savings. Considering how much you spend to get there and be there, I personally wouldn't stress out over a calculation that will change your total trip cost by only $20, or even $100. Go, spend your money as you desire to enjoy yourself and then do enjoy yourself. Have a great time.