I've got a lot of things I'd like too... I see a lot were already covered, but here are a few I can't see.
> Move your cursor over a spot on the car and be able to highlight those layers, like with an outline around them on the car and on the layer list. I've had so many times I've been looking at a squiggle or gradient or whatever but not been able to find the layer in the list!
> Select a later on the list and make it highlight where it's visible on the car model. I always end up with lots of covered-up decals when I'm finished and it's a pain going and deleting them at the end, and also I often delete one from where I can see it in one spot but I don't realise that part of it was showing in another spot.
> Stop resetting the camera view every single time I go to move a layer.
> Copy layer and be able to paste elsewhere.
> Transparencies! An alpha gradient would be nice.
> An option to "stretch" the area of a patterned decal but not re-scale it, I mean like you apply it to an area and it tiles the pattern. E.g. this would be for carbon fibre effects, pinstripes, half tone patterns, etc.
> Change the projection of a layer after you've applied the decal.
> Change colour of a decal you've just chosen without having to place it, go to the colour picker then back to resizing the layer.
> Move the layer you're currently working on up/down in the layer order using the d-pad or something, rather than placing the layer then re-ordering it in the list.