Timeline

Right.... at the very least, they return to a world where their contributions happen much earlier, with the differences those events caused, plus an extra set of eyeglasses, dated to be much older then they look, causing all sorts of confusion to collectors.

Thats what I'm basing my question off of - the whole concept of time travel that i like / support / use - timeline rewrites. Not predestination paradoxes, and not parallel universes, so agree to disagree on this point. I think the "the real universe still exists" people are just trying to justify their own desires.... one timeline, different events happening due to time travel butterfly effect, effectively replacing the old events. We saw this with "City" and "Yesterdays Enterprise".... sure, there might be parallel universes too, but those are totally different things then affecting your own past and its casual effects. This type of time travel is used, for instance, on the show Fringe, and in movies like Back to the Future, or 12 Monkeys. If this wasn't the case, there wouldn't be any huge drama/importance to restore the timeline to its proper form, and it would be unfufilling to think that the bad future you sacrificed to restore still exists out there... the whole point to that type of story is that if the hero succeeds in changing the past, the bad future will no longer exist. Old Spock and Nero were the remnants of the old timeline, the temporal causes of the rewrite, and thus, as the "traveler" they were protected from the rewrites to the timeline. Any events before that incursion, however, should be untouched, including previous excursions to the past, as those events still happened in that earlier era (1930s and 1960s in TOS, 1986 in TVH) as they were not touched by the rewrite that occurs from Kirk's birth forward.

Obviously, the theoretical questions i'm posing depend on accepting the rules for this particular time travel theory. ;)