Layering sounds (vocal tracks in this case) and treating these tracks in a different matter can certainly give some interesting results. I haven't done eq-ing a vocal track the way you described, but I can see what benefits could be had. Like Dan I wouldn't see it as the way to do every (vocal) track every time; only when absolutely needed.

Some songs just ask for a certain kind of extra sound to them. A thickened vocal can give you that extra bite where needed. So layering tracks can be very useful. And above all; it is fun to experiment with these kind of things

Mike
www.mikewever.nl