So I bought the OPI Sand polishes as soon as they came out. I got the blue and purple and was lucky enough to find them on sale for $6 each. I swatched them immediately and thought they were pretty neat. I even put a top coat on them to see what they would look like and enjoyed them that way too.
I later preordered 2 of the Pixie Dust polishes at $8 each. Knowing these were close to the Sands, I ordered the red and gray. I immediately regretted the gray and thought I should have gotten the black but have since appreciated my gut decision.
Below you'll find a split imagine with one of the Pixies and one of the Sands. The top is two coats of each and the bottom is two coats of a top coat over two coats of each.
I have been going back and forth but I think my final decision is that I like the Pixies a tad better. They are not quite as gritty and contain no larger glitter like the Sands. However, once a topcoat is applied, the Sands are more glittery in the sunlight than the Pixies but the Pixies only need two coats of a top coat while the Sands really need three. Overall I say that these may be similar but definitely the same. If you can, own both, you'll appreciate them differently for sure.