Yep, contrast is king, also not turning every slider on the scale to 100. (For anyone out there doing their designs). Also, only add black when you want to really add black. A cymk file is a Subtractive color file. You are never adding color "on top" of white, you are "removing" white from showing through. Every bit of color takes out brightness. Combine that it a non standard printing surface (this material) and a non standard printing method (dye sublimation) and the affects are even more noticeable. One of the best things you can do when you're happy with what you see is turn your brightness way way down on your screen and see what you think. The less backlight, the closer to reality (kinda).. then convince yourself to make this part an little brighter, and that part a little brighter. Btw I think they look fine, and the design element is nicely done as well. "Ghost" items (e.g. your race tracks) are always tricky and you really only begin to get it down after many many prints.
Also kick ass Raiders.
Trade you any of these for some ncv arcs 
