Nice has more polished meaning. It's seems like the meaning is on the surface and don't touch the basic core of the character.
Kind is more raw, more primitive and this is the best word to describe the noble of the heart.
"He seems nice" = show the possibility of friendliness, politeness, and manner attitude.
"He seems kind" = show the true character that u can be sure of. U know that he's reliable, trustworthy and helpful. It may brutal from the outside but very gentle on the inside.