Obviously you have never ridden a bike with wheel spacers on a motocross track. Also, the suspension travel is staying the same, but you are moving the tires away from the bike like aftermarket a-arms would do, increasing leverage, so the valving of the shocks will need to be adjusted for that.
Ive seen PLENTY of wheel spacers break on heavier, faster quads riding HARD. If you are just putting around a MX track then you might be fine, or you might not. Its your health you are risking, not mine.
This is like putting +2 a-arms on a bike with stock shocks, only you are cheating and adding something that is now the weakest link in your suspension, and its a much weaker link than the weakest link of your previous setup.