The other attacks you describe all derive from the fundamental reason I declared all non-proof-of-work systems to be insecure back in April.

My logic was mathematically fundamental. The input entropy set is quite deterministic and well known and thus can be preimaged. For example, accumulating a lot of coin-days-destroyed and then targeting them in clever ways to subvert the security.

The randomness (entropy) of each proof-of-work is fundamental and mathematical and it can not be preimaged. It can only be surely defeated with > 50% of the network hash rate. Note I recently offered what I believe to a solution to the selfish-mining attack (the one at hackingdistributed.com that claims 25 - 35% attack).

I am skeptical that you can characterize all possible attack vectors of proof-of-stake in one coherent mathematical proof. Thus you will not know formally what the security is; instead a list of adhoc attacks and counter-measures.

Nevertheless I am not bagging on Peercoin. Everyone should be free to decide for themselves which coin they prefer. Perhaps there are unknown attacks on Bitcoin as well, yet I am somewhat comforted by the clear math for security of proof-of-work. I will not say I will never be convinced to support a non-proof-of-work coin, I will correct myself if someone explains such a system convincingly. It is on my TODO list to study more Peercoin.

Edit: Perhaps coin-days-destroyed in some attack vectors motivates not transacting for long periods of time.