We tried to eliminate rabbits in Australia by introducing myximatosis. There are still rabbits, but myximatosis runs rampant.
Humans are not a single organism, we co-exist with a number of other organisms, many of which live inside us in our guts. Without them we would die. Actamel call this "good bacteria".
It is impossible to irradicate a virus, infact virus' already have a natural predator called the phage. Phages evolved at the same speed as virus', it's a natural cycle - when a particular bacteria blossoms so do the phages: Like foxes and rabbits. However mutagen rates are fairly constant and sufficient to allow numerous evolutionary paths for any given bacteria at any given time.
Extra terrestrial life is quite likely to exist, we make this deduction based upon the sheer scale of the universe and the fact that, right at the bottom of the food/organism chain, amoeba's employ fission to create new life and do so under conditions which are recreatable in a celestial sense. Therefor logically life does exist, and has done at different times in the life span of the universe (afterall, Mars was once where Earth is).
Therefore we can also make the deduction that, on a universal scale, Humans are absolutely inconsequential, and indeed if there is a God then Humans clearly are not the intended end-goal (on the ground that we cannot survive indeffinitely on Earth because Earth itself will die, and if we travelled planets we would be exposed to different environmental conditions which would favour further evolution).
Infact with the impending energy crisis, shifting of the jet stream and other ecological evolution and social dellapidations in progress it's quite possible that the Human population will suffer a significant population decrease within either our lifetime or the life of our children. Not that i'm a subscriber to the Jehova's Witnesses or anything, we've already survived plenty of doomsdays - but i'm building to a point here.
Krakatoa is a volcano, and in 1883 it had a very famous explosion. However geologists also believe that it had a much bigger erruption around 45000 years ago. When I say much bigger, we're talking super volcano big - like the one under Yellowstone in America (that's a bit overdue). Now factoring in the rate of genetic mutation it is possible to estimate the Earths Human population at the time of this erruption based upon the gene variety in the world today, the estimated Human population of Earth 45000 years ago is 15000. It seems we dont do too well against super volcanoes, and we're due one anytime.
So I ask again, just what is meant by "important"? I think if you ask the gaia we live on, the answer is "only me".