I am sure that many species have disappeared unnoticed over the years. I seem to recall some attention on this site about the spotting of a very rare specie of Woodpecker a year or so ago.
At times, in my mind, it seems hard to balance "progress" with the need to preserve these creatures. I think you’re correct though in saying that the attention towards preservation increases with the appearance of the subject to be preserved. The Desert Tortoise gets a lot of attention, while people gripe at the environmental studies that stop the housing projects because of a sub-specie of the desert Kangaroo Rat that might be displaced. The pressure upon these decisions will only increase as the planet fills up.