The iPhone 6 would never boost long-term prospects for market growth, because it's not meant to be. It is a product category already existing within the world with Android phones that are, as statistics state, already dominating that market. Google, on the other hand, has the real long term prospects with their operating system being open sourced.
Apple needs marketshare not short term profitability...But they can't get the marketshare, and in fact is losing marketshare. IPhone 6 wouldn't be able to reverse that trend, not by a substantial amount anyways.
However iTunes would be Apple's trump card, their only gateway to long term profitability... But even people aren't switching over to iPhone just for iTunes... It just hasn't reached that kind of level yet.
Plus most of the profits gained by Apple over the last quarter are mostly people buying multiple phones or buying them to sell to the secondary markets, or upgrades, which wouldn't gain marketshare. Yes they are earning the profits but Apple isn't gaining new customers, and especially in China and developing markets.