The Reason why the body piece when upgraded goes from Blaze Spikes -> Shock Spikes, is so that if you do get hit, the Shock Spikes could proc and Stun the mob for a short period of time, thus meanin ya could get Utsusemi back up more easily.
Not to mention that +5 Dex improvement is really nice in terms o' gettin Acc and Crit+ 8P