Prudent and Bitcoin are two words that don't belong in the same sentence. You never know when and if you're in a bubble until its too late, but the ludicrous growth isn't a good sign of stability.
Either way, the "correct" way to spend BTC/ETH doesn't seem to be via a series of transactions made via a VISA, does it? Why would go not go directly via an exchange?
How does selling at an exchange, eating a 1.5% fee, waiting 4-5 business days for your ACH transfer to clear, then using that money in the bank to send a payment to pay a normal credit card bill get you want you want faster, easier and cheaper?
With this, you can escape large parts of the banking system and control more of your own money in a more granular way if you choose to.