Bit-depth reduction is counter-productive. You're just adding noise to the signal, and reducing the dynamic range.
As for resampling, it depends on the specifics of the resampler used by a specific codec implementation. If a resampler is terrible, it could add artifacts like ringing and aliasing that would degrade the encoding quality.
As for resampling, it depends on the specifics of the resampler used by a specific codec implementation. If a resampler is terrible, it could add artifacts like ringing and aliasing that would degrade the encoding quality.
A great souce for resampler comparisons: http://src.infinitewave.ca/