It really depends what you want from the bike. For me as a 365 day London commuter, my priorities are reliability, weather protection and getting noticed on the road. So the keys mods were:-
Crash bars, hugger, fender extender, super loud Stebel air horn, Meta alarm, Fazer Thou rear brake caliper, stainless pipes, Givi rack, hard wired camera mounts.
Next up some consideration I've got some yellow wrap to try on the headlights, braided brakes lines, also thinking about a Scotoiler and fork gaiters.
Not sure if that's what you had in mind, but ones preferences between form and function often differ.