Since the credibility of the website http://www.novaccine.com/ has been brought into question in this debate, I hardly see how continuing to post it in discussion messages constitutes spam, which is generally defined as unsolicited commercial messages.
Yes, one might take a narrow view of this site's spam policies in regards to multiple postings of URLs, perhaps especially if the one taking such a view found that the site ran counter to their bias, but I hardly think that the WM would consider it being spam in this instance.
BTW, I happen to believe that http://www.novaccine.com/ is a very credible website, for the same reasons Mira has posted. Given the credentials and links she has posted about the site, I would consider it far less biased and far more respectable than sites such as Gorski's Sciencebasedmedicine, Quackwatch or Skeptoid.
As the name implies, http://www.novaccine.com/ is about giving the downsides of vaccines, but does so in a science-based and well documented alternative way with well credentialled contributors. Those other sites give obviously biased views given by mainstream apologists with far less credibility and credentials.