Why is "son" used here (vs. esta)? I had understood "son" to be used for permanent conditions and "esta" for temporary ones.
My grammar book says "The use of 'ser' with an adjective denotes that the speaker considers the quality signified by the adjective an essential . . . . component of the noun." I think the idea is that your are emphasizing the current 'newness' of the shoes, rather than "Yeah, they are new now, but they'll wear out."
That's right. I believe it could said, it's down to emphasis and that's all.
If somebody says "mis zapatos están nuevos" normally would be a situation where the shoes ARE old, or never used but look new.
I guesse you right about it. That's exactly how we would say in Portuguese, which is very similar to Spanish.
Ser is used for qualities. It least thats what i have be told by a native speaker...