Indeed, Solanas's work is a diatribe. It's a manifesto. Consequently, you will not find citations and more often than not, you probably won't find much to hang your hat on for solid ideas. You will, however, find broad generalizations and "ranting." What's important about Solanas' work is that she wrote it in concert with what she felt and saw around her during the late 1960s, the time of the nascent radical feminist movement. Her manifesto is an extreme expression of some of the frustration and, in some cases, rage that women involved in the movement felt about institutionalized and personalized sexism. The SCUM Manifesto, therefore, is best considered as part of the primary documentation that emerged from that historical period. Even things readers might consider odious or vile are valuable because they provide insights to the more extreme aspects of issues which are always tied to mainstream movements.
Solanas herself was a deeply troubled woman who struggled throughout her short life with the remnants of abuse that she suffered during her childhood (I suspect sexual abuse, given her deep-seated rage against men). She was quite prolific, writing short plays during the 60s that she would perform at impromptu venues. She eventually attracted the attention of Andy Warhol, who probably found her intense, bright, and with an acidic sense of humor. He agreed with some of her views about sex, but ended up losing one of her play manuscripts (her only copy) and this may have set her off to commit a more violent act. In 1968, Solanas shot Warhol with a .32 caliber pistol, prompted by her own demons and what she may have perceived as ridicule from Warhol and his associates. Warhol survived; Solanas was sentenced to 3 years in prison; the SCUM Manifesto was eventually published in 1971 as a result of media attention surrounding the shooting. Following her prison term, she seems to have dropped out of the public eye and continued with her life, heading west. She died in 1988 of pneumonia in a welfare hotel in San Francisco.
The Manifesto is a reflection, therefore, of Solanas' own past but also offers some insight into what she perceived around her as the power of men over women, institutionalized and expressed sometimes in violence against women. For its reflection of one woman's experience (as deranged as she herself may have been) with the transformations going on in 1960s American culture, it should not be dismissed. But it should absolutely be taken with a pound of salt.