I think there is a pretty easy to distinguish difference between 'SEO spam junk' and 'non notable' but if you're worried about that you could always have 'non notable' default to all outbound links to be 'nofollow'. For every problem there is a solution, if you want to solve it. I've seen and heard just about every excuse possible why particular things should be 'non notable' but not a single one that has stood up to scrutiny, it always seems to in the end boil down to 'because we say so'. Which is a pity because ultimately 'notability' is as much in the eye of the beholder as it is something objective and what is non-notable to one large group may well be notable to another. And if that first group is over-represented amongst the wikipedians then that's the end of that, no matter how important something really is.