More people will really be willing to buy a $300 console for Donkey Kong in 2013? I disagree. Maybe at ~$200 where families wouldn't feel bad about getting it for their kids, but I really don't think DKC has the power to sell hardware to casual gamers. Metroid, on the other hands, appeals to a completely different subset of the audience. A smaller, but more dedicated subset who will spend more on gaming.
While you have sales numbers for Metroid Prime that could disprove this... nothing can really be said about what Donkey Kong Country could do in terms of selling hardware. The userbase for Wii by the time DKC came out was huge. There was obviously interest, but if no one gave a shit about Wii, I feel DKC would have bombed and failed to move any significant hardware. Metroid would have obviously bombed too, and in the end the distinction is probably pretty pointless... but I really feel like Metroid would do more good for Wii U than DKC at this point.