On a long thread there can be an awful lot of thread creep. I think I would rather see a long-dormant thread come back refreshed as itself, not a Part Two right away, so people will actually read the first post and go from there. If itt attracts a lot of new attention then a part two can be created soon after.

But if it's started with a part Two, I would rather see the frist post from part one repeated, than the stuff from the end.

~Susan