I'm not really sure about the answer of the question of whether intelligence is a gift or a skill. I know that I had an easier time in school than most people around me did, but I also know that I had more supportive and nurturing parents than some other kids did. So whether or not I was 'naturally' more 'intelligent' or whether I had just learned to be better at academics than them, I don't know. I do genuinely believe, however, that some people have better memories than others, and that this does play a factor in potential intelligence. Remembering is an important part of learning, so a person who can remember better is usually capable of learning better.
As for the ethical questions...
Most people seem to ascribe to the philosophy that an incination to be smart is something your born with. But if that's completely the case, wouldn't be wrong to insult someone's natural intelligence or only reward people who were born with a better advantage?
To insult someone's natural intelligence, perhaps. You could argue that it would be a bit like mocking someone for a disability (that is, if intelligence is, in fact, something we're born with or without). But to 'only reward people who were born with a better advantage'... I would say there is no ethical dilemma there.
Working with the assumption that some people are inherently less intelligent than others, would it make any sense at all to treat everyone as equally intelligent? You mention that the smartest kids get the best education - but why shouldn't it be that way? If someone is borning lacking in the area of intelligence (again, I'm not suggesting that this is the case, merely rolling with the assumption), does it make any sense to give them access to the same education as those gifted with intelligence? After all, aren't the 'gifted' going to be able to make better use of that education? I mean, this may sound callous, but why waste a Harvard education on someone who isn't actually going to learn much from it? Why shouldn't Harvard be reserved for those gifted few who are going to make the most of their time there?
I think a fitting analogy would be a basketball team. As a general rule, basketball players tend to be pretty tall. There are exceptions, of course, but it's the general rule. The reason is that height provides certain advantages which are good for basketball players to have in order to be successful at the sport.
But height is definitely a genetic trait, with no skill involved whatsoever. Nobody 'works hard' to be tall. They're just either tall or they aren't. Does that mean that it is unethical for a basketball coach to work mostly with taller players? I'd say definitely not. That coach is merely taking the players who have the most advantages because the players with the most advantages will be best for his team. Why should he spend his time coaching a midget when, in all likelihood, that midget will never possibly be able to perform a slam dunk no matter how much training he has?
I'd say the same would apply to intelligence, if it were a natural genetic trait.
A rocket scientist's education shouldn't be wasted on someone who will never be able to be a rocket scientist.