How much cpu/gpu power is required to just confirm transactions? I don't think the difficulty of computation is going up proportionally to the increasing number of transactions that are needed to confirm.
The same amount. Transactions are confirmed BY ADDING BLOCKS TO THE BLOCKCHAIN. That's the same process that mines bitcoins. So, if you want transactions confirmed, you have to "mine" blocks by adding them to the blockchain.
That process can also never stop, or transactions will stop being confirmed.
However, there are built-in "rewards" for continuing to mine, even when you no longer get paid any BTC for mining them. The miner that finds a block and adds it to the blockchain gets the transaction fees for the transactions initially confirmed with that block. In theory as Bitcoin becomes more popular, there should be more transactions, and therefore more transaction fees for the miners.
If the transaction fees are insufficient to attract miners, then miners will drop out. As miners drop out, the difficulty of finding new blocks will decrease, making it easier to find blocks, allowing miners who ARE mining to find blocks faster and therefore earn a larger number of transaction fees.
It's actually quite elegant.