Are 4GB DDR5 128 bit video cards still worth keeping in order to mine ETH based blockchains over the next 3 months?

What seems to be used for centuries to store value in a secure way when it comes to precious metals seems to come in handy here is well: vaults. When it comes to "perfect cold storage", I think that the term "perfect" is overrated. Any security policy is as weak as its usability requirements restrict it to be.

For example, even a vault needs some usability in order to be a viable solution for storing your paper wallet.

Ultimately, it all boils down to the actual amount of stored value. Certainly different volumes require different security approaches.