It doesn't really matter whether or not NPR "needs" federal funding, it shouldn't receive it, no matter what the amount.
NPR loves to claim they only get a tiny sum from the Feds, and maybe they are being truthful, but you can bet that they spend time and money keeping political relationships that will continue the income, in good standing.
NPR and PBS are a whole lot more "commercial" now than ever before, but there isn't anything inherently beneficial to the common good in non-commercial media.
Non-commercial media is not free. The folks who produce it don't and wouldn't do it if they couldn't make a living at it, nor should they.
Everyone benefits from the tax-payer supported armed forces. Everyone benefits from tax-payer supported highways (whether or not they drive on them). It's even arguable that everyone benefits from agricultural subsides (although there's a lot of room for debate there), but an argument that everyone benefits from tax-payer supported news and entertainment media or art is specious at best.
Does anyone believe that a national referendum on tax-payer funding of NPR or PBS would result in continued funding?
Therefore, in order to support its continuation, a credible argument has to be made that it actually is a benefit to the public at large. Such an argument cannot be made.