b&w n vs d money better spent on amp?

If you stay with the N series and spend the saved money on better amps, then you will wish you had the diamond series. It's a catch 22.

I replaced the plastic phase plugs in my 805Ns with solid copper ones, which brightened the sound and evened the amplitudes over the dynamic range. With the Cu plugs I find the 805N to be superior to the newer 805S, which I compared intensely back-to-back over 3 hrs in a listening room.

Perhaps you can find some simple, inexpensive tweaks like this for your 802Ns that will bring them closer to the qualities you like in the 802D.