Once bitcoin has replaced VISA, you'll probably not make a substantial profit of bitcoin anymore, but you'll still want to buy it because of the utility it brings.
Can the bitcoin network support the volume of transactions it would take to replace VISA or any other major credit card? The Visa web site says they process 150 million transactions per day
http://corporate.visa.com/about-visa/technology/transaction-processing.shtml. Is there an practical upper bound on the transactions/day for the bitcoin protocol? I imagine the block chain would get enormous very fast at that volume, but I'm still a newbie so I may be missing something.
Currently about 7 transactions/second is the Bitcoin limit, but will be increased later. Block chain is still very small, about 12 GB, it is nothing with today TB drives, and for normal person client version without blockchain downloads are avaiable like Electrum
hard drive space is not the problem. the problem is that with larger blocks is that it gives big advantages to miners with high speed internet connections and incents people to join larger pools. inotherwords it would cause bitcoin to become more centralized.
i think this problem will be solved also, but trying to brute force a solution with larger and larger blocks is probably not wise. there are proposals that could potentially make each transaction smaller and centralized but trustless off chain ledgers that use bitcoin for clearing could take over the load for smaller transactions.