Re: The BTC price is too high for it's current security model

1) The attacker can attempt a double spend
2) The attacker withholds a transaction to cause economic harm

Incomplete list, and you are ignoring some very important implications.

For example, withholding transactions isn't just a question of economic harm, it can also be used to whitelist/blacklist.

Better analysis here: http://hackingdistributed.com/2014/06/16/how-a-mining-monopoly-can-attack-bitcoin/