I think Jayne is right about dinner with a group of women being a bit trickier than a date. Is your friend (and her friends) likely to be as interested in, and knowledgable about, fashion as you are? You've also mentioned that the restaurant is in a casual neighborhood with an focus on "rustic" Italian food and communal eating. That skews pretty casual and down-to-earth to my way of thinking--sort of like pulling apart loaves of bread with my hands and drinking wine out of tumblers instead of linen napkins and crystal wine glasses.
The point of the evening is to have fun, so I'd pick an outfit that maybe had one interesting, cool aspect but was relatively "safe" in other respects. Great shoes, to my mind, would be a no-brainer outfit focal point that would totally go over well with a group of women; a short leather skirt might be trickier. A cool sweatshirt could be another no-brainer focal point while a fancy, glitzy designer shirt could make you stand out quite a bit if everyone else was dressed more casually. But, hey, I'm quite a bit older than you, and probably more cautious, so take my thoughts with a huge grain of salt.
