In general i sell all those things i can get a good price on when i am really sure i will not need them again..
Never could get a good price for my Kurzweil PC3x, that got replaced by the KRonos, however, it now makes a perfect mainstage controller, i have combined it with the PA4x... and the KRonos, its currently getting less used.. Which prooves that sometimes reliving old gear can be great fun...
But in general, i try to buy used stuff, so i can even make a profit of it if i decide to sell it..