Oddly enough was just having this discussion over lunch.  Dirty is harder.  You need more detail in your texture maps and nodes, you need to model in some of the bigger dents and broken bits.  Flood-fill rust textures just don't make it.

It does feel like shiny and new is more attractive to the buyer, though.  Even though, to make a shiny and new object look nice, you still have to apply some fingerprints and small blemishes and so forth!  (My current set has material nodes that add a bit of dings and other noise).

If I was sure it would sell, it would be my choice to at least offer, if not design around, a more battered look.  For some things, this does seem natural; I can't see anything Old West looking like it just came off the Wells Fargo Wagon from Sears, for instance.

But I'm making some musical instruments right now, and I can't see many customers really being attracted to the dented, broken valves, duct-taped joints look.  Certainly not as a primary.  But is there really enough interest in the market to even make this sort of texturing and detail available as an alternate?