Ford Focus spoiler or no spoiler?

[ChristopherZX5]

I have this brand new ford factory painted spoiler sitting in the garage:



I can't decide if I want to install it or sell it.

I like the way it looks but not enough to go ahead and put it on without regard to how it may or may not effect fuel economy. I know the only way to know what effect it will have will be to try it and find out. Installation will require drilling holes in the hatch and that is just not something I am willing to do unless I am sure that I want it to be a permanent part of the vehicle.

I was hoping to get some theoretical knowledge as to whether the spoiler will possibly help, hurt, or have no real noticeable effect on FE. I typicaly drive mostly highway at 55-60 mph and occasionally reach the speed limit of 70 mph if I am running late for work.

Here is my car now:



Hear is a similar car with the spoiler:



So what do you guys think?