All three Metroid Prime games combined: 4.4+ million worldwide.
Donkey Kong Country Returns: ~5 million worldwide.
There was one passionate dev on the web who called for Retro studios to do another Metroid
The games seems to be on top of the charts so much people can still see potential, and I agree.
It was reported all over I belive though I've seen it just vaguely, i'll try to find the article.
Many many potential customers of WiiU may be welcomed by this, it's not what you call a new IP, but it's a very good launch period booster for the core market.
If they could remaster it with fixes and also slight improvements and all the stuff that can be done without having to re-do stuff or call in big resources, I think there's a ton of things that a few programmers can do, texture resolution is a tricky think if they have the higher-res raw source they can easily use less compression.
This is not a case of remake begging, I have never done this (okay in past, recently it was only majora's mask but that was due to rumor), I think Metroid Prime deserves it most and genuinely, and it deserves it way more than all of those other remakes.
I'm pretty sure the first Metroid Prime out sold the other 2 by quite a bit.
They we're all a stable 1.5 Million, which proves in the second two the fanbase never left and was coming back to buy the new ones.
Original prime did 2 million because it was sold as PAK in Europe.