to tell the truth mp isn't needed for psy if you want try to awake your boots with like 1x mp and then try out your dmg and see if it's any difference ^^. psy dmg is based on atk/int and int based mp :P ^^
But you can switch with psy as well from Mp to attack to get the best dmg so Mp is actually a bit needed. Its like with just atack suit you hit about 400k and if you do switch eg from mp to atack you will do more than 500k so i think its pretty usefull.