I, personally at the moment, would never buy a cashcard. I paid $80 for GTA V because I got the Special Edition and while I enjoy playing online very much, R* has not done much with the game, after Online launched. A Beachbum DLC pack that didn't include anything really special, A bunch of new game modes called 'Capture' that are decent but are not so special. If heists or any other worthwhile DLC pack is released by R* and has a postive response within the community, as well, my own liking, I would not have much of an issue buying a cash card to support R* and any other projects they have lined for the future.
Yes, GTA V has been a rough period for R*, and not everyone is satisfied with how Online ended up or where It is currently now. But still, this is the same company that made all of the other GTA series games which everyone more or less grew up on and remembers highly, RDR which was beyond an amazing story and awesome game. This is just a very rough patch in the road for R* right now.