I have a very, very hard time believing the halving of the block reward is going to double the price.
Some believe that block reward drop is already baked into the current price.
What's more likely to happen, if ASICs aren't out yet, is the BTC network will lose a lot of hashing power and possibly implode.
Nobody knows the minimum level of mining capacity and its distribution that would still protect against an attack. It has been estimated, however, that if an attack was done for financial benefit (i.e., using the attack to carry out a successful double spend) then it is more than 10X more powerful than is needed to protect against that threat. (i.e. it would cost millions of dollars to carry out an attack that would yield, at best, well under a million dollars worth of financial gain.
The reason the amount of hashing is so high is not that bitcoin needs such levels, but that the block rewards provides an incentive for this level of mining. There's a big difference. If hashing power drops in half after the block reward drops in half, we're still probably just fine.
