Personally I collect the cards instead because I have a tendency to revisit cities years into the future. I just wish cities wouldn't make their cards expire so damn quickly. Wuhan's metro is nice, the cards don't expire until 10 years later. But I've found Singapore and Taipei expire within 3 years and you lose your stored money.
I have this "brick" of public transit cards for about 20 cities. It feels powerful. I kind of wish I could just swipe this brick in any city and just go. Unfortunately they all interfere with each other.