The difference between a 50% win rate and a 58.3% win rate is, on average, one card in the vault.
So if +3 upped cards will increase our win% by more than 8%, it is a risk we should take.
Hopefully you have a FG grinding deck, so 3 upped cards in 3 days wouldn't be a problem.
If anyone is completely unable to grind for 3 ups, please say so.
Also, is coin now able to use 6 ups in each battle?