Right now I'm really picky with P2W but might purchase one at a sale. I actually locked myself of what I can spend. This is 100 or less of my local currency.
For gems, I haven't spend much, only like 20 or so. I have about 300 and I still have no idea what I'd purchase it on. Right now, gems appear in crates, on rare ones and higher. Its not worth it to purchase the vault as it only has 6 sets of cards, 2 of each, from common all the way to epic. And comes at a max capacity of 300. If only the price can be reduced in exchanged for having the vault's capacity larger. You'd pay like half the price and have the vault raise its minimum capacity. Once its full, which makes it slower, it can easily benefit an entire alliance.