The idea that love is a response to the value of a person's rational nature will seem odd so long as 'rational nature' is interpreted as denoting the intellect. But rational nature is not the intellect, not even the practical intellect; it's a capacity of appreciation or valuation--a capacity to care about things in that reflective way which is distinctive of self-conscious creatures like us. Think of a person's rational nature as his core of reflective concern, and the idea of loving him for it will not longer seem odd.
J. David Velleman, "Love as a Moral Emotion," Ethics 109 (Jan 1999): 365-366.
I would only make one caveat to the above, namely, that this is only one thing that can legitimately be considered love; even love as a moral emotion. It's an important one, of course. I like it that someone gets the point about what talking about 'rational nature' really is -- the point that, for instance, led the scholastics to say things like "Man is a rational, and therefore social, animal" as if it were completely and utterly obvious that a rational nature is a social nature. But the sense of 'rational nature' that really is capable of the role it plays in ethics, politics, and the like, requires seeing the richness of what it involves. And Velleman's conclusion to the article, "love is...a moral education" (p. 374), is exactly the right one to draw.