What I'm taking as a cue here is the symbiotic relationship between humanity and dogs.
'More intelligent' aliens, well, we'll be the dogs - we will be at their mercy. That after all, is the ultimate implication buried within 'more intelligent'. Yet, dogs are not entirely at the mercy of man - the relationship is too deep, too broad, and holds too entirely different points of view (dog and man) for such a pithy summation to be inadequate. Aliens of 'equal intelligence' (equal power) can't be a greater risk than ourselves - humanity is already at risk of wiping itself out of existence, I don't see how a coequal alien race could really create a scenario that much more terrifying than the Cuban Missile Crisis. If nothing else, maybe by then humanity would have world leaders who stayed clean. And like with dogs or the many other less-powerful species we've eradicated, the only risk a 'less-intelligent' alien species poses is a moral one. Would humanity add xenocide to its list of confirmed crimes?