That it is true, if unintuitive, that people gain moral worth the more "real" they get, is a position I have seen on LW, and the arguments do seem reasonable. (It is also rather more coherent when used in a Big Universe.) This post assumes that position, and includes a short version of the most common argument for that position.

Incidentally, I used to hold the position you describe; how do you deal with the fact that a tortured copy is, by definition, no longer "part" of the original?