I hadn't thought about using the nappy roller as just a way to transfer bulk paint to the surface where you use a foam roller to spread it out. Cool. There are many ways to do this and I am sure there are some new ways to be discovered.

That said, according to the conventional wisdom if you are getting runs, you are putting on too much paint for your mixture/conditions.

You are looking to lay down a thin, smooth coat that won't require as much sanding. The depth of color comes from the multiple coats and if you didn't have to sand as hard between coats, it is much easier to lay those coats down.

I think charger said his wet sanding took like 30 minutes to do the whole car (correct me if I'm wrong). That would only be possible if the paint has laid down smooth.