I've seen UFOs twice.Would you like to see a UFO? Really? You should be careful what you ask for.
The first time I was a kid and saw what looked to be a double row of red lights moving horizontally across the sky, but see-sawing as it moved. My younger sister saw it too, but the last time I asked her about this, she says she doesn't remember it. The second time was more like what you described: mysterious yellow balls that were dancing around overhead in an overcast sky with a distinctly 'non-ballistic' motion. Eventually one joined up with another one, and they all disappeared. This was seen by a whole line of people standing outside a movie theater (25-30 people).
The first one could have been a hoax. The second is harder to explain, because, as you say, the lights had no feeling of solidity to them. They seemed to be 'glowing balls of light.' The first one in my first sighting seemed to be a solid craft while the second ones didn't. They seemed like some inexplicable light phenomenon.
Anyway, though, I was not rattled by the experiences anywhere near as much as I am rattled when there's an earthquake here. I find earthquakes to be profoundly disturbing experiences.