Still doesn't change the fact that it is a complete pain in the rear when another AST overwrites your buff. No matter your own self awareness. Sure people can educate others, but it would be often enough to set up a macro for it and half the time you'll be greeted with a "don't tell me how to play my class" response.

As for actual suggestions...
They shouldn't stack if they are the same card in my opinion.
If they are different AND from another player, I don't see the harm. I think the RNG element is enough to not make this too overpowered, most of the time anyway.

They'll have to do something with the cards for Shadowbringers anyway, due to removal of TP and therefore making the current Spire redundant. Someone suggested on another thread this could become a direct hit buff which I guess is the last remaining stat to receive attention thus far.

Also, do savage/ultimate/extreme organised parties typically NOT have 2 players of the same class and therefore this isn't a problem for them anyway?