I don't think that's the way it works. Gain != resolution.

The theoretical S/N and dynamic range limit of 16 bit audio is 96 dB. Maybe you are confusing analog and digital gain? The further away the peak digital signal is from 0dBFS, the lower the dynamic range. Less dynamic range means the difference between softest and the loudest parts is reduced. This increases noise. As noise increases, details is masked and resolution is reduced. Achieving 16 bits worth of dynamic range will yield more resolution.

Even if the mastering hardware didn't have as much true resolution as 16 bits would tend to indicate, they would still adjust the compression and gain correctly.

Well then, GIGO! If the material in the mastering process doesn't achieve 16 bit of S/N and dynamic range, then what use is there in increasing the gain after the fact? It's not going to remove the added noise or add dynamic range.

And in my experience, the discs in my CD collection, including the old ones from the 80's, are all within a few percent of 0db. There are exceptions, but they are rare.

I must have quite a few "rare" 80s CDs. I believe I read you saying you liked Depeche Mode. Try ripping and normalizing Music for the Masses and see what happens. Another one is NIN Pretty Hate Machine. Of course there are many others from all genres, but you get the idea.

Stu