You confuse me when you ask why PoS would help a coin's economy though. PoS/PoW/Premine/etc. have nothing to do with the economy; they have to do with security. Bitcoin has a high enough hash rate behind it that the security really isn't an issue (unless a government decided to crash it). KARMA, on the other hand, could benefit from the security, since it's more vulnerable. But this has nothing to do with the economy and it has nothing to do with the price. You can have the most secure coin ever and it have 0 value, or you can have the least secure one and it be worth billions.
It's likely that any system that potentially effects the number of coins in circulation would effect the economy. PoW, PoS, PoC, (premine), etc.
It's a large part of the reason you may not get high interest rates at your bank. The Federal Reserve (if you're in the US) wants you to spend money to grow the economy.
PoS is not only about security but also the economy.