well, both are basically naturally occuring. it's not like we're talking about education, or fake tan - both of which are attempts to distort the natural being, to improve them via alteration - but rather intrinstic qualities with which to make value judgements.
both are essentially impermanent, but it's beauty (in the traditional or mainstream sense) which fades first. yes, our minds eventually become less agile; but it's usually a long time after a person has passed the upper age limit which defines beauty (i'm not proposing such a limit, but merely identifying society's desire to do so). so in a sense, attractiveness could possibly be viewed as a more ethereal, less lasting quality - as doofqueen has noted.
i think the key is that intelligence is inevitably linked with conversation and thus company: our social interactions are what define us. no matter how much you love someone, if you spent 60 years just looking at each other it would be fairly dull, i'd imagine. interactions define relationships at all levels, from friendships to official negotiations, from divorce to the initiation of a new romance... and our ability to interact is always linked with intelligence.
this is, however, misleading... as we know, intelligence is so much more than the sum of its parts. emotional and intellectual intelligence are different creatures; people can be incredibly intelligent yet harbour no real conversational skills - their brain is tuned to some other wavelength (be it musical, mathematical, autistic) which means that communication is a different experience for them, and that they seek to express themselves differently. in each case, however, that different intelligence will be attractive to others, because it's just another factor. at the other end of the scale, some people can talk forever without saying much (i'm one of them).
i guess the key is not differentiating between intelligence/attractiveness in a binary sense, but realising that our attraction to people is composed of a number of interdependent factors, liminal and subliminal - some of which we don't even recognise outright, such as pheremonal interactivity. i would tentatively suggest that as long as there isn't a huge intellectual mismatch - an incredibly bright person and someone who finds brainwork uncomfortable and unwelcome - a relationship can easily prosper, and intellectual distinction would be just another one of the filters we use when identifying people we'd like to be with.
it's considered more superficial because in a sense it is more superficial... beauty is generally instantly comprehended; it can be enjoyed at leisure, but that first-impression-physical-presence thing will never be as lasting the intellect.
i'm reminded of a quote that of all the arts, architecture works most slowly, but most surely, on the soul... intellect, the subtleties of how someone's mind works, is something that you discover slowly, a process that's far more revelatory than simple show-n-tell physiology. discussion, insight, response, debate - these are the threads with which we weave the tapestry of our image of the Other mind, and they are active and critical, rather than reactive - there is a vast difference between thinking 'ooh, nice legs' and 'i really had never thought about [topic] that way before'.
the flipside is that intelligence and beauty are generally things we consciously and subconsciously present to the outside world, playing to our positives and masking our negatives, constructing a persona - us - with which we interact.
IMO, the process of engaging with someone's mind is the true act of love.
