It entirely depends on your needs, whether it’s cosmetic or adds features.
I can still share the components and plugins I use on all (or almost all) my own forums.
Plugins:
Data Explorer: always useful as an admin.
Who’s Online: it’s a nice touch to inform people that there is actually other folks browsing at the same time, and it fits my communities sizes
Discourse Yearly Review: adds a bit of fun 
Discourse Locations (unofficial): I use it on my trading categories.
Components:
DiscoToc - automatic table of contents: great for guides
Inline PFD Previews: it’s convenient
MD Topic List Mobile (unofficial): greatly improves the topic list on mobile in my opinion