A polarizer is a very specialized tool. I probably use mine once or twice a year and I don't shoot landscapes.

As for dust - here in the Midwest it is not really a problem so I can hike all day with no lens cap, no filter and still not have to brush it off. Granted I always keep the lens angled slightly downwards when carrying it. Even with snow I don't usually have a problem as long as I'm using a lens hood - I just have to remember to knock the snow that accumulates on the inside of the hood.