Technically speaking, altering the suspension geometry in such a way (for visual reasons as opposed to an engineered improvement) has a negative impact on handling and the longevity of all related components. Think about holding a gallon of water out in front of you compared to hanging it on the end of a broomstick and holding the stick. Though its pretty much the same amount of weight, the change in geometry would put much more stress on your shoulder, elbow, wrist, etc... Granted that is a very exaggerated example but the principle holds true for wheel spacers, wider than stock wheels, and altering the ride height. The question is: Do these minute alterations create a difference any normal person can detect? It would seem that the answer is "no" considering the other replies to this thread...
I'm not against suspension mods and plan to lower my FX when time and finances allow, I just wanted to throw my $0.02 and say that there technically are "cons" to wheel spacers.