The fact that ZERO PoS systems have been attacked, even though many of them are tiny, speaks volumes about PoS security. ALL of your attack vectors remains a theory at best. If you want to prove your point, the best method is not theorycraft further, but actually go and attack one currently public and working PoS system, you can even pick a tiny one if you wish.
I'm not blackhat and won't go around commiting crimes to prove a point. My logic is sound and eventually some blackhat may perform a NaS. I don't believe NaS is a likely attack vector for PoS and never claimed as much however ignoring the possibility is irresponsible.
I don't want to get into another discussion with you about Bitshares, since it's pointless to discuss Bitshares with your vivid imagination. You are calling a community voted and approved change by the developer team an "attack", that's just too funny. Can I call Gavin's "block size" increase of 50% per year an attack? I didn't even get to vote on it. I would have preferred another way of handling the block size, damn I'm now alienated and upset!
I would consider anything that strayed from the central tenets of Bitcoins purpose/ideals to be an attack. Increasing the transaction volume was actually an intended improvement while some investors where sold that Bitshares was a "true deflationary" currency by many promoters including yourself which is a big deal.
BTSX recent short term price drop compared to Bitcoin isn't even my main concern but the trust and credibility of the currency is now tarnished as new investors will always wonder when/if /and how much the next devaluation will be.
If BTC would ever increase above 21million than it would be catastrophic and many in the community would not consider the new fork "Bitcoin". As you suggested, security can come in many forms and not just the algorithm itself and the fact that Bitcoin is a certain size, has first mover advantage, has enough developers, and has a community with certain ideals (I.E... we will not inflate the currency supply) are tremendous security aspects one must consider.