I used to really enjoy theming and Riceing, but then I realised it was pointless: my monitor always looks the same, with a full screen IDE window covering up all my fancy themes
I think that speaks to another aspect, individual apps taking full control over how they're presented instead of inheriting whatever framework the DE is providing or the cohabitation of various KDE/QT/GTK/X/other, or electron framework defaults. Over on windows even when uxtheme skinning was in full swing it was the start of applications doing it themselves (winamp and quicktime come to mind), but I have the impression developers doing so made sure the extra effort had a payoff.