The single most important thing you can say about a work of art is that it is real, that the artist to whom it is attributed made it. Until you are certain that a work of art is authentic, it is impossible to say much else that is meaningful about it.
As would be expected, most commenters followed John Quiggin's lead in denouncing this claim, pointing out that the artwork should have some worth outside of its provenance. And I certainly agree with this. But then I read a comment by Bad Jim, who asks a provocative question:
"Does anyone even bother to try to fake music from folks like them [Brahms and Schumann]? And if so, why not? An original manuscript of Mozart’s variations on “Twinkle, twinkle, little star” would be pretty damned valuable; how much more would his noodlings on “Happy Birthday” fetch?"
This is an excellent question, and one to which I didn't know the answer. I am familiar with the probable forgery of Shostakovich's memoirs, and of the Joyce Hatto plagiarisms. There are certainly pieces that were once attributed to someone famous, like the pieces in the Anna Magdalena Bach notebook that are now believed to not be written by Johann Sebastian. But those were honest attempts that were corrected as more facts became known. The closest thing I can imagine is David Cope's EMI project, but he was always upfront about the provenance of the Chopin-esque or Bach-ish pieces his software composed.
Let's assume there haven't been any serious attempts to forge a piece by one of the masters. There certainly is motive for doing so, a Beethoven score sold for $2 million in 1991. There certainly is a large amount of expertise needed to create such a forgery, but that is the same with paintings. Is it because the forger would need to be a expert at composing in the style of a master, and be an expert at copying the handwriting of the master, two very different skills? Certainly a painting forger has the single skill of painting in the style (yes, there is brushstroke vs. structure vs. color palate vs. materials used), but that is all still very closely related to the art of painting. Whereas a music forger would need to master the counterpoint, melodic construction, orchestration habits, notational idiosyncrasies, paper and ink properties, handwriting, and means of properly aging the score. A team of experts would be needed to carry off such a forgery, cutting down on profits and increasing the likelihood of someone getting caught and spilling the beans.
As it turns out, there is a history of musical autograph plagiarism, at least in the 1930s. A man named Charles Weisberg forged scores by the American composers Francis Hopkinson and Stephen Foster, and sold them to various collectors during anniversaries of these composers. He was caught, thanks to the efforts of musicologists and rare book experts, but his efforts have apparently caused some havok to music librarians, according to this article in Notes: "Forgery in the Music Library: A Cautionary Tale" by Gillian Anderson, et al (Vol 60 No. 4, June 2004), 865-892. Apparently the forgeries were not good at all, being copied from Sousa marches and Rubinstein's "Melody in F", college fight songs, and an opera by Grétry. The only reason Weisberg had any success at all was due to the lack of fame and ability of Hopkinson. Musical ability that is, he was a well-known satirist and a signer of the Declaration of Independence, which is why his scores were collectible.