From a seminarian:
Just a question: Is it permissible for those candidates to be installed as acolytes during their seminary formation, in addition to the alb and cincture, allowed to wear an amice?
Of course it is. And it really must be used when the alb is designed in such a manner that your street clothes are visible. Street clothes need to be covered. Aside from the traditional theological meaning of the amice, as the "helm of salvation", it is a practical garment as well: it hides street clothes and it helps to keep vestments clean.
This is a non-issue when serving in a cassock and surplice.