Sadie often gets muddy, especially at this time of year. I prefer to wash the mud away but shampooing weekly is too much, I just rinse off the muddy parts with water.
I find that Sadie needs to be brushed from approx. once every to week (for about a half hour) to once a month. I don't know if its all of the brushing or what, but she never seems to smell like dog. I bathed her on Sunday because on a hike she fell into some stagnent water and her white rough was looking grey. She went for 4 months without a bath and I would have been happy to let her go longer.
Milo, my parent's sheltie does get that doggie smell but he has a very thick coat and is only brushed when he's groomed (every 2+ months).
My advice would be to bath as little as possible (when Sadie was a pup I bathed her once a month, sooner than that made her itchy and her fur dry, even with oatmeal shampoo), brush as often as you can and use a spray on doggie deodorizer.