I'd like to think that anyone who was been starved for Metroid content wouldn't pass up a chance to play both.
They're both versions of Metroid II though.
I recently decided not to play through Skyward Sword because there might be an HD release in the next year or so. I don't want to play through the same basic game twice in a relatively short period, I'd rather knock something else from my backlog.
Similarly (and I don't think I'm alone in this one) despite it being one of my favourite games, the announced Shadow of the Colossus remake, despite looking cool and very faithful to the spirit of the original, left me somewhat cold. Mostly because I just played through the HD version earlier in the year. Now I'll probably end up grabbing it cheap in a few years.
Sure, the fanatics will play both, I played through AM2R and will get SR day 1. But if even a single person skips it because they only recently played 'a version of Metroid II' then Nintendo has lost out because of what is essentially an illegal product. AM2R wasn't just a conceptual IP breach either, it included a lot of stolen assets too.
I really, really don't understand why people capable of making a good game do this to themselves. Strip the stolen stuff from it, make yourself a new character and now you have a cool product you can actually sell. But then I guess the IP infringement is the only thing that gets them attention in the first place.