I'd argue PoS miners are much more security minded, since they have to pretty much keep the wallet hot (online), even if briefly, in order to mine with it (though I believe in DPoS system you don't have to, since mining is delegated to the delegates, you can put your funds in cold storage). Also they are very much de-centralized, instead of concentrated in a pool, can you imagine how hard it is to obtain the identity of 10,000 PoS miner, their IP address, and then some how access their mining PC etc...
I'd be much more worried that discus fish and ghash.io getting hacked simultaneously (imho a much more likely scenario) and the attacker instantly gain 51% in Bitcoin.
You put forward some good arguments and I think that it is inevitable that we'll have to move from PoW to something more efficient down the track. I guess the next thing is to work out "which kind of low-power proof is best" (btw - I have a new one that is neither PoW nor PoS but is as energy efficient as PoS - you'll have to PM me to discuss that).
That sounds great, but you'll need to first implement your concept in an altcoin, so that it becomes a "proven" concept, otherwise I doubt it can be considered as a choice.