I personally don't see the difference between a burnished and a nice conditioned uncirculated. it's literally a buffed die that imparts a bit more luster to the strike,and kind of hard to tell the difference between the two visually if the bullion uncirculated is just a really good strike,.
I dunno, I think it was just a way for them to add another mint product for collectors to buy, I mean it's the difference between a satin finish, and a slightly more satiny finish in my opinion, but the burnished carry the W mintmark and that is the major difference.
maybe a burnished collector will disagree with me, and can point out the differences but Personally I don't see it from a well struck bullion that's in really nice uncirculated condition.
it's like the satin finish mint set coins and the circulation strikes, I don't see a real difference there when you compare a nice business strike to the one in the mint set.