bowser took me a long tim to beat too, i just kept dodging him, letting him run at me, running behind grabbing his tail and(try to) throw him in to the spike ball bomb thingys, and after i thin you hit him twice some of the area your fighting him on breaks off and it turns in to a star shape floor (to make it harder for you to throw him into the spike things...)
as for getting all 120 stars, yes there is point to it.