I just got v1.6.0 today, and everything's working fine except the gold coins appear as tiny silver/gray coins that are hard to see, and don't rotate.
This sounds like a problem with your Neverball installation.
One possible cause of the effect you're seeing is that some of the contents of the data directory from 1.6.0 have been accidentally overwritten with those of 1.5.4 (specifically, item/coin). Make sure that you have a clean install of the official 1.6.0 files.
In case you have custom/add-on game data installed in your Neverball user data directory, you may also want to check that those files don't contain any old coin SOLs or textures that would override the newer ones.
PS: Is the cats eye ball supposed to be overlayed with the classic one, because that's annoying too, but not game braking.
Yes, that's intentional. (Behind the scenes, it's not actually a case of overlaying the two balls. Rather, the design decision was to use a variation of the familiar checkered texture for the surface of the cat's eye ball. There are other examples of this, such as the snowglobe ball.)