Does the resampling and bit-depth reduction of the wav file actually help? My intuition is that a modern encoder like Opus will work better if it has more information.
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.
