It's always interesting to read about what "dirty" brass might do to dies. Of course, if you're picking brass up off the ground (either yours or somebody else's) that's one thing, but just firing brass doesn't make it very dirty.
Depends what and how you're shooting I guess; almost all of my brass hits the ground, unless it's from a Ruger #1 or a revolver. I have scratched dies (yes even carbide) from dirty brass (meaning dust/dirt/whatever), and find it no significant trouble to drop cases in the tumbler with some case polish.
On the other hand, squeaky clean brass is not desirable other than for looks; I prefer to have at least some case polish or wax residue left on them after tumbling. I haven't switched to stainless pin tumbling for that reason.
