So even if we couldn't take our physical bodies out of their existing paths through time... this limitation might only be limited itself to the corporeal elements. Our consciousness's, however, need not necessarily be chained to the same restrictions.
Obviously this is not a new concept, not even close, and the wealth of stories out there - in both fiction and factual studies - shows that this is already a well-explored concept.
But still... just think - maybe the reason why we've never had any evidence of time travellers from the future is coz we can't actually see them. WoooOOOooooo... Or even better... in the future, they've discovered how to piggyback their consciousness's through others and ride backwards through time in that way... reliving the past through our eyes. Unable to change anything, but able to get firsthand accounts of what really happened...
Somebody might be looking through your eyes right now........ =D
So if you ever see me looking at the mirror, and waving hello.
Now you know why.