Without going into the origins of what people see as UFOs, why do you think aliens wouldn't have technology far more advanced than what humans have at present? As I stated before, I believe there could be species, literally, billions of years more advanced than humanity, given the sheer amount of time since the Big Bang and since the appearance of (what I believe to be, maybe incorrectly) conditions similar to those that gave rise to life on Earth throughout the universe. Maybe we will still meet a lot of species at roughly our technological level in the future, but I doubt those will be the majority - I mean, ask yourself, what will our advancements look like in 100 years? 1000 years? 10000 years? They might have had billions of years more than us to make those advancements.
This is pretty much the same argument I make when having these kind of debates. Also, isn't it self-evident that any alien beings that can visit us have superior intellect and technology to us?
Most likely, of course, but not necessarily - or rather, we can imagine a few (unlikely) situations where that wouldn't be the case, either for those that actually visit us, or those that, even though being able to do so at their will, aren't far superior, as DarkHyudrA suggested (of course this would probably be better suited for a Startrek episode, but still fun to imagine).
So, for example, imagine the species that actually arrives to visit us is the equivalent of the microbes in Voyager (I'm kind of referring to this comic:
http://what-if.xkcd.com/117), though not necessarily at that stage of evolution - and it's anyone's guess whether or not the species that actually built the ship is still around, or if it even evolved beyond the point they where at when they launched it. Another possibility: they built a generational ship, countless millennia ago to travel the cosmos, but their culture/society/technology wasn't able to flourish under the new conditions, perhaps leading to losses in many areas - hopefully the ship would be mostly automated and able to self-repair.
Yet another possibility: they have indeed developed some form of interstellar travel (not necessarily FTL), but are generally much less intelligent than humans, and simply made up for it with the extra time they've had to develop (as in, they appeared much earlier).
Or maybe biological life as we know it simply can't evolve far beyond a certain point. Biology does have its limitations, and also imposes limitations on our intellectual abilities - who knows how far we can actually reach. Perhaps we're already very close to our limits (I doubt it, but while we're imagining).
And then we can also imagine life that is simply quite different from what we know: maybe some are almost completely spaceborne, but primitive; or some may be technological, but just so different from us, that they didn't follow our developmental track; and so on.
