Definitely time for a new seat.

As for the numb toes, I had this problem too. I also have Nike shoes, and switched to Specialized thinking it might help. Nada. So then I got a professional fitting, and the guy moved my cleat all the way to the front, using the first set of holes on the shoe. I thought this was too far forward, but it worked! I still get a little numb, but far less often than before. Before, I had them sort of in the middle. Guess that was too far back. Also, it helps to wiggle your toes every once in a while, BEFORE the toesies start to get numb.

HTH!