I think if 7Soul wanted you to look at existing tilesets, they would've linked you to a site specialising in those. Don't draw inspiration from other tilesets if you want to do something unique. Draw inspiration from reality! Mix and match aspects of different strange places on earth to create your alien world. Study what's common on our planet, and you'll know what to avoid or to build a "twist" on.
There are also plenty of photos from the surface of Mars, and artists' depictions of alien worlds based on scientific data which might be helpful if you're interested in creating a realistic alien planet.