Let's just say, hypothetically, that there was an abandoned wallet with, like, $150,000,000 worth of BTC in it.  Say, one of Sheep's.

• How long would it take to find the private key and gain access to the coins?  For one machine, or for a pool?
• If everyone got together and formed a pool, and split the payout, would it be worth the energy costs?
• Is there a difference between the difficulty for SHA256 and Scrypt with regards to wallet private keys?
• Are there any cryptocoins that are particularly susceptible to wallet private key attacks?