Are perfect forgeries aesthetically equivalent to the originals they copy?
There are two types of forgeries: reproduction and imitation. Reproduction means copying a painting exactly and then passing it off as an original and imitation means copying the style of an artist and then claiming that it is a lost piece of theirs. Traditionally forgeries are not given the same artistic merit as the originals they copy even if there is no visible difference between them. If we are to claim that the original is aesthetically better then this implies that there is something other than the paint that makes up the aesthetics of a painting.

In 'Languages of Art' (1976) Goodman argues that our knowledge of an artwork's history affects the way we look at it and so even a hypothetical perfect forgery would be different from the original copy. Goodman states that forgeries are not aesthetically equivalent to the originals because even if you cannot see a difference, you could learn to.

Dutton (1979) agrees, claiming that the aesthetic properties of a painting are defined as both the sum of its parts and the place in art-history that it takes up. This is because each piece represents a performance by the artist and so a forgery is a misrepresentation of this performance, this translates into an aesthetic difference even if both paintings are physically identical.

Lessing (1965) proposed that forgery does not occur in the performing arts because it requires faking originality and in the performing arts originality is not required. Lessing argues that context only shows who is a better artist, not which piece of art is aesthetically better. Lessing claims that to prefer one over another on aesthetic grounds is simply snobbery, a perfect forgery is a moral and perhaps historic concern but not an aesthetic one.
       
Lessing's argument explains why reruns of plays are not seen as forgeries, although this only applies to reproduction. Goodman argues that an exact copy is not counted as a forgery, because a painting is autographic whereas mass-produced art such as music and literature is non autographic or allographic.

An interesting example is Andy Warhol's mass produced art, even though it was mass produced, similar to the way that CDs are, it is still autographic since each factory produced piece is individual. If I copied his work using my own screen printing machine it would not be a Warhol, whereas if I copy a CD or write a poem by someone else then it is still that of the original artists. Allographic art is abstract whereas autographic art is more tangible. Imitative forgeries rarely happen in music, perhaps for financial reasons, although it is possible that in 50 years time a 'lost' Beatles song will emerge much in the way of the 'lost' Vermeer paintings forged by Van Meegeren did.  

References

Dutton, D. (1979) 'Artistic Crimes: The problem of forgery in the arts', The British Journal of Aesthetics, vol. 19, pp.302-341.

Goodman, N. (1976) 'Languages of Art: An Approach to a Theory of Symbols', Hackett, Indianapolis.

Lessing, A. (1965) 'What is wrong with a forgery?', Journal of Aesthetics and Art Criticism, vol. 23, pp.461-471.