I think the white cars in particular is a problem. To help with the depth Id try adding a lot more contrast. make the deeper bits darker, but also add some contrast with the hues.
Here, I hope you dont mind, but after I saw the reference pics I carried on fiddling with my previous edit:

From the pic I interpreted the body shape rather different, more like how you did the blue one (benneton? I don't know!).
To add some depth I've tried to add more contrast in the pallette as I described above.
Where I mentioned about contrasting hues - if you look at my pallette, the mid tone is a plain red, but the highlighting colours shift towards orangey yellows and get more saturated, and the shadow colours shift more towards purple and less saturated. This seems a fairly common trick but it instantly helps with contrast and vibrancy. I've also made the greys more bluish, and the white more greeny yellow. Pure white always looks a bit flat to me, save it for the highlights on the white cars.

Basically on those I'd try to use the same technique, exaggerate the depth on them, dont make the bodies pure white, just use that on the shines, and steer away from using a flat grey on the shadowed areas.
I wouldnt worry too much about remodelling the bodies like I had, I think the blue one and the super aguri's bodies in particular look good.

I'm really just mentioning techniques I've picked up from others here, but hopefully It'll help!

I really love this, one of my favourites I've seen in a while. The colours are particularly lovely, and I really like the chunky outlines. It all seems pretty purposeful to me, looks like hes wearing gloves, and the shading on the head is the same as the gun, I guess 'cos its shiner than his suit.
Id like so see him in a little scene.
The only one crit I can think of is perhaps his left wrist could pull in a little tighter, a bit more like the original lines.

Im guessing so that objects such as your little guy there ar displayed properly, your coders will have some sort of check in place to see how high each tile is. So at least it shouldnt be too hard to do a height bonus.

Thanks jmgandalf, thats very handy to know.
When I said copy/pasting I actually meant from where I work on the image into photoshop ( I use gamemakers image editor for all pixelling ), although come to think of it I think I did copy from my browser at least once so despite my battle to stop it I may well have contributed to the darkening myself without realising!
Again thanks for the tip, I'll keep that in mind in future, hope others do too.

Yeah really lovely. Quite similar to some plans i made for a game but never started. Hope you do get your project revived, it'd be a shame to waste these. Some aa on the black under the beams would neaten them up a little, but otherwise very nice.