thanks for the mention…
but, yeah, i should add… “sweetening” is one of those words like “mojo” or “warmth” that can mean different things to different people.
for me, and my day job (as a mastering engineer) i think of “sweetening” as more of a question… “what does a track need?”
sweetening is not always ADDING, either… in fact, adding is secondary in (my) mastering to subtracting and sometimes taking care of a problem (frequency, with EQ, etc) will enhance, and thus, “sweeten” the mix.
there are some processes that are harder to put your finger on and describe and can often be used to great effect to make a mix sound better in a few different ways… saturation is one of those “mysterious” processes… i find different kinds of tube saturation can give a mix girth… or “hair”, or a lift… or just a little something that’s sort of difficult to describe.
but, to echo @abalone it’s definitely not just the gear, but knowing what needs (wants/should) be done to a mix to make it sound… “better” (? subjective) and then how to do it… having certain tools that either make your job easier or don’t harm the audio more than help are somewhat secondary…