Actually, these "non-nailed" blocks would work really well in a sort of toy themed level. They appear to look a lot like a child's building blocks now, and I'm sure that a few users could benefit from. I would recommend a few more with other colours like red, yellow and maybe even purple. That would pull off the effect being colourful toy blocks very well. A simple edit, but highly effective, well done Koolkat!
It's funny how some edit makes everything seem different...
I like how everyone's now starting to look more inside the box and only modifying the graphics slightly rather than going for full-blown new graphics. Here, it seems to have been pulled off to good effect, and can go well in just about any SMB3 overworld level, even without the nails.