Sargent seat, muffs, tobinators made the biggest difference to rider comfort. Should probably add the Rukka suit to that as well, though it's not exactly a bike mod.
Steptoe Head protectors, for those little 'moments'.
zumo loaded with tunes, autocom and kenwood mean nice things to listen to and I can talk to my girlfriend when she's riding her bike too or answer her call when I've stayed out longer than expected enjoying the ride, and find my way home when I've followed a few roads that just looked fun.
Wilbers rear shock, transformed the handling (80k on the original)
HID's, probably the best night time safety option, given I ride country lanes to and from work.