Haven't had a problem with mine. Were shiteloads better than the Nangkangs that I threw away as far as ride. If the potenza's are better they'd be almost super soft (could explain Shano's 050's wearing unevenly at 32psi).
And if it was just a decision between the Nangkangs and Yokohama's, for the extra $200 a corner I'd be going the Yoko's every time. How old is your "brand new" spare? What would you be using as a spare were you to buy 3 to match your current spare?