That's not even the main impact. Think about all of the people accessing Wikipedia every day - students, teachers, randoms - who don't read or watch the news. Ever.
All of these people who will probably never hear about SOPA, even if it's passed, will suddenly realise that their First Amendment rights are under threat and will hopefully be incredibly, incredibly angry.
I don't think the mainstream news media cares about Wikipedia. Plus, the site's process and product are a direct challenge to the legacy news oligarchy.
Eh, I would say (sadly) that the mainstream news media practically depends on Wikipedia to fill in background info for half of their stories. Gaffes by TV reporters have occasionally been traced back to Wikipedia vandalism. Sometimes Wikipedians then cite the misguided journalist(s) when adding the falsehood into the article [1], a circular phenomenon of "fact-creation" that has been lampooned by xkcd [2].
That is cynical to the point of being shortsighted. Even assuming the "news oligarchy" really operates as something resembling a unified entity, and regardless of said unified entity's feelings vis a vis Wikipedia - an outage would make headlines.
I am not saying all editorial coverage would be uniformly supportive, but it would certainly be newsworthy.
If Wikipedia is locked out for a week, it will make mainstream international news in no time flat.
I think it needs to happen.