PoS provides:
-- additional security (different source of blocks)
-- reward for long-term adopters and holders
-- economical stimulus to maintain a full node
PoS if implemented won't spoil Quark monetary model (0.4% or 0.5% inflation p.a. is a little price)
PoS don't even connected with price or a position on a graphics. It's pure techical issue, an additional layer of security, an important one on a low hashrate.
PoS suffers from a "nothing at risk" problem. An attacker can use coins they no longer have but did have at one point in the past to attack the network. Actually there is no reason to not do this.
And this is serious. Need to do some research.