Except that transactions that are smaller than 10 kilobytes do not currently require a fee. So the user can probably create a transaction that contains nearly 100 inputs each at 0.00005 BTC. That would be nearly 0.005 BTC worth of 0.00005 BTC inputs that would be spendable in any one transaction.
But a transaction with a 0.005 BTC output triggers this rule:
Code:
// To limit dust spam, require MIN_TX_FEE/MIN_RELAY_TX_FEE if any output is less than 0.01
... so you're back to paying 10kilobytes * 0.0005 BTC / kilobyte == 0.005 BTC to spend those 0.005 BTC.
Yes, if you have a large-value, well-aged input then you can combine it with tiny transactions, have a single output greater than 0.01 BTC, and probably get into a block for free.
If you want to prototype a smarter coin-selection algorithm, you might start with the 'spendfrom.py' code I wrote as an example of using the raw transactions API:
https://github.com/bitcoin/bitcoin/pull/2162