I used to be of the opinion, "don't sell your sh!t, ever!".
But:
I sold my '89 Norlin-era lefty Les Paul Custom, purchased brand new, which was my main axe during my early band/gig days.
I don't miss it at all.
I also sold my '88 Marshall 100W 2210 head, which was my main rig during my early band/gig days.
I don't miss that, either.
I've sold other crap I've used in the past... Zvex Nanohead, other amps, pedals, geetars, countless crap.
Truth is, I don't miss anything I've sold... well, except the Rockman 1/2 rack unit stuff (still have my X100B Rockman though).
I have far better stuff now than I ever had before.