the fans do technically have a life span. more speed = shorter life
they could start to whine or make a little more noise, but if you dont mind that then whatever.
they wont break or anything, it is just typically good practice to not run them faster than they have to be run.
power supply shouldnt really make that much of an issues fans typically dont use that much power, if heat is not an issue the main reason i like my fans slow is for the quiet. my case has 3 80mm fans on my gpu, 2x120mm fans on the cpu and 2x140mm,1x200mm and 1x120mm case fans with them turn right unless im gaming my 7200rpm hdd is noisier than all those fans combined