I don't think the 560 is meant to be a good value vs the 150-450... you buy the 560 simply because you want (and can afford) it.
In NIkonland, there's the 200-500/5.6 and 500/5.6, and the reasons people prefer the 500 is that it is smaller and lighter than the 200-500, has better AF, and is a bit sharper. For us, the sheer size of the 560 makes the decision more ambiguous.
I still want the 560 though
Earlier this summer I seriously contemplated buying the A* 600/5.6, but chickened out and got the K 500/4.5 instead.