By the time we figure out how to travel through time, we have established a temporal prime directive that explicitly denies us the pleasure of going back in time and making a fuss about it. In other words, there may already be some time travellers among us from the future, but they don't make it known.
If there are any here on earth right now, they are most likely here on a mission to prevent something bad from happening that seriously jeopardizes the future, and have found a way to evade the paradoxical situation that once they prevent that from happening, they were never sent back in time to prevent it from happening, thus it happened, which caused them to be sent back in time to keep it from happening, etc.
I doubt it, though. We are far from being advanced enough that anything we do now will have any effect on whether or when time travel technology is discovered, developed, and applied. There have been no hypotheses or blue prints or models of a time travel machine as of yet, so there is nothing about a time travel machine or the idea of a time travel machine to disturb, disrupt, or alter. So, coming this far back in time would be mostly pointless, unless this very thread, or even my post here is what causes the time travel machine never to be invented. *suspicious look* (I gotta get a smilie for that)