It's probably better to thoroughly clean fabrics treated with DWR ( Durable Water Repellency) than to let them get too dirty, Dirt and grime will break it down more than the occasisonal toss in the wash. Even on the most expensive shell fabrics, the DWR needs to be renewed once in a while. A toss in the dryer will reactivate it to a certain degree.
I'm not talking waterproof fabrics like Goretex. I'm talking about some of the less expensive water-resistent nylon fabrics. I have friends who put their jackets in the washer and dryer with every wearing and then wonder why the garment doesn't repell ANY water.

I've found rinsing or sponging keeps these types of garments grime free and in better shape for years and years. And, if iI need Goretex to stay dry and clean, I stay off the trails and take my Goretex fishing. I've got all kinds of garments including Goretex waders and jackets, Activent, you name it, and my stuff lasts forever. Matter of fact, I wish it wouldn't last so long so I would have an excuse to go buy more.