On the Decals, I use Eagle One Nano-Wax Spray. Works great and the decals look like new after 2 years. Never leaves film or streaks. A lot of us are using the Nano....Enjoy.
I tried the Mother's back to black and you are right, it is greasy and attracted dust like a magnet.Wash and dry. I use Mothers Back to Black on my Daytona Decals, it's a little greasy.
Otherwise I just throw on spray wax or detail spray, just make sure you read the label to make sure they are safe on Vinyl. Dont use wax liquid or paste or they will get streaky looking and ugly!
One thing to watch out for with the application of any product on the vinyl is what the vehicle (what keeps it liquid) is. Any product that is greasy, oily contains silicone. Silicone dissolves and degrades cast poly vinyl choloride PVC. Other materials from store bought contain petroleum distillates. This is a BIG no no as PVC is made from petroleum. Also any type of wax is a build up product and can act like a magnifying glass on the surface concentrating and trapping the suns rays.....like burning ants etc.