To quote an ex cop I was talking to, "Never buy an ex cop car".
He was referring to all kinds of thrashing and abuse. Anything from chases, Hitting speed humps at speed, potholes etc etc. Wherever the bad guys went the cop cars would follow and at whatever speed the bad guys were going..
Anyway, back on topic, if you think you would get more for a 2006 Omega because there's a 1.4% chance it was an ex cop car... go for it. You might convince a P plater with that story and he would proudly go and tell all his mates as well.