Doesn't work that way, bitcoin proof of work uses SHA256 twice, which is of limited value. It gives you a near collision to a double hash. It's burning energy for work.
One could make a case that the use of sha256 would drive down the cost of comodity ASICs, enabling a well resourced attacker to use mining hardware 'off-label' to find sha256 hash collisions. Same goes for scrypt, with the adoption of its use as a password store.