The first question I have is why is an XRP currency unit needed in order to keep the ledger of IOUs? That's not how Ripple started...
XRP are functional component of Ripple. I gave some details above. Pathfinding is essential for cross-currency payment. Liquidity only need exist between XRP and each external currency. Having a cost associated with ledger entries helps prevent ledger flooding attacks, as well as the small portion of XRP destroyed in every transaction.
Second, if you say XRP currency was created to raise money I don't have a problem with that, but it should then be done as an alt-coin, the cryptographic model people are familiar with and respect because they know there are no shenanigans for the market. Everything is independently verifiable.
Ripple not having mining was an intentional design decision, to increase computing efficiency and network speed.
I recommend watching the interview with Chris Larsen linked earlier in the thread. He is candid about the targeted utility of the network and immediate business plans.