Primarily my coroplast bullnose piece. It didn't look as good as I hoped (definitely didn't pass the wife test), also the aero design was flawed.
http://ecomodder.com/forum/showthrea...ast-23162.html I also have a roll of lawn edging and a bunch of fasteners I bought for one idea or another and then thought better of it before I started fabricating. For instance at one point I thought I would do an air dam located behind the bumper, but before starting got to thinking about where the deflected air would tend to flow and decided a lot of it would end up going under the car, and so it might even result in a drag increase.
So generally my false starts have seemed to be more about bad aero design than construction method. But my motive for changing the tried-and-true ecomodder designs was for simplification of the construction or some other factor. I see why that was a mistake, now I want to do it right.