I'm probably going to get ripped a new one for my comments, but I firmly believe that there is no wrong way to do something on a model if it gets you the results that you are looking for.
Example #1:
For this build, I layered different colors with a brush (no primer), and then rattle can for the final color coat. Some careful sanding until the base coats revealed themselves, and one last coat of flat clear. Some strategic dry brushing doesn't hurt either.
Example #2:
This was my first attempt at a rusted Junker. Again, I layered different colors, both acrylic and enamel over each other. Next, I splattered some Micro Mask (aka liquid masking tape) and let dry. Rattle can enamel top coat, and then used a toothpick to pry off the Micro Mask. Some light sanding in the "oxidized" areas too.
If anything - going against the rules of mixing acrylic and enamel probably helped me get the distressed effect I was looking for.
Personally, I've never tried the salt method, but have seen great results by those who have. From what I read, if you do use salt or hair spray, using acrylic top coat is probably necessary.
Only useful advise I have is to go experiment and have fun.
Going to quote Bob Ross here when it comes to weathering cars: "there are no mistakes, only happy accidents!"
SC