How about them adding colour specific chests to the tower and colosseum?
Say a 40% chance that a coloured chest will spawn in lieu of a regular chest of the same quality.
At least then you'd be able to have improved odds of hunting a card, especially at higher tiers. It would also make for tactical choices: in the colosseum - go for more points or go for an easier chest that has a chance of drawing a card you desire. I'd rather have my odds reduced to 1 in ~16 over 1 in 77.
in the tower - burn or spend diamonds to open a chest when your slots are full. When the odds are low for a common card, I accept burning the chest and taking the initial gold.