If you are traveling at a constant speed of 80 mph, it would have the same effect on handling assuming you had the weight positioned correctly in the car. I don't think the added drag from the deployed spoiler would be enough to affect the handling. At any other speed, the spoiler will produce different amounts of downforce, so you'll get different handling results. As far as acceleration, you would get different results depending on how the added inertia of the weight compares to the added drag from the deployed spoiler.