There is a teshuvah in Igros Moshe that says that just as with mitzvos like shofar and lulav, women can optionally put on a tallis. However, it depends on her intentions. If to really acquire extra kedusha or zchus, then it is ok. But if it is just to show that she is the same as a man, then not ok.
At any rate, I have always wondered why women would feel inferior when they have the mitzva of raising the next generation of yidden. Why is that less important or meritorious than wearing black boxes or a woolen cloth?