If you're just a regular person, you shouldn't be trying to make millisecond-timing decisions. But you can absolutely say "thus-and-such appears to be systematically underpriced" and make a decision to transition some funds toward bargains.

I recognized there were bargains to be had in March of 2009. I didn't hit the exact bottom (March 6), but I got some pretty nice deals on March 12.

Right now, I wouldn't go out of my way to make excess contributions. The signal isn't strong enough. But sometimes it is.