It does look a little too schizophrenic. It would be nicer if it was a bit more clean because right now its just too much took look at.
That box thing you have going in the viewport seems to have a lot of emissive spots for the sake of having emissive spots. They don't really add anything, imo.
As for lightmass,
here's the official article. Just Ctrl+F "LightMassImportanceVolume". Its a volume that lets you control the emission of the photons (number of bounces, etc), intensities of AO Spec, and other stuff like that.
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