There has been a lot of praise for the N802 speakers over the years, the Diamond series are not necessarily a big improvement over the regular Nautilus series. I believe these two factors are making the N802 speakers worth having, even at a premium price. Just my opinion, I would love to hear other peoples thought on why the N802 have become so expensive on the used market.
Personally I use N801 in my system (Oppo 105, Krell HTS 7.1 and Krell TAS) and they sound great to me.