When I gear up for metallic reloading, I decided to go the wet tumbling route. I have since learned that wet tumbling can make the brass "too clean". By "too clean" I mean that the brass can gall and seize particularly in the expander die. I was feeling this effect in my single stage die sets but it became a big issue with my Dillon SDB, especially with 45ACP. Dillon said to polish the expander die and use case lube both inside and outside the case. After doing these things, the seizing dodes in fact go away but its likely that you wouldn't see it on dry tumbled brass due to the residual carbon as mentioned above. It is a problem for new brass as well. I went a little overboard with the polishing because it was fun and I learned a lot. My trials and tribulations are in this thread here:
Brass deposit form vertical lines on Dillon powder funnel
I think either wet or dry tumbling can be made to work but wet tumbled brass (or new brass) benefits greatly from some case lube: Hornady One Shot, Dillon Synthetic, DIY Lanolin at 10% in Red HEET fuel treatment. I've tried them all and they seem to work about the same.
LOL, I wish I had read this recently. My tumbler broke and I just bought a Franklin Arsenal wet tumbler. I probably should have stayed with the crushed walnut! But the wet is better than trying not to breathe in the air from around the crushed walnut when you are pouring the brass out. Bummer ither way.