IMO reverb is a last resort in Mastering .. usually you are trying to re-reverb a song with reverb in the mix .. so 'unifying the songs' can be problematic this way.
Also, IMO, when I hear 'sheen', 'sparkle' and 'air' I think of the two aspects pointed out below as concerns how it relates to mastering, along with a clean mix (as mentioned above; no mud!). Used prudently they add life to cymbals, vocals, guitars (especially acoustic) and the mix in general. They help things sound more 'live' as opposed to a narrowed bandwidth recording.

/ducking before the puritan firing squad starts





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I do not work here, but the benefits are still awesome
Make your sound your own!