There have been clawed hammers since at least 1514: http://en.wikipedia.org/wiki/Claw_hammer

Clearly, innovation is good - the modern (1514) hammer is better than the big stone our Homo Abilis ancestors used. But at some point, you reach an upper bound.

It was a separate innovation, followed soon after by a different innovation to combine a claw tool and a hammer tool into a combined tool.

But there are other things you can put on the other end of a hammer besides a claw, none of which made the original hammer a bad idea if all your problems really are nails that you don't need to claw back out.