re: Points to keep in mind...
The movement seems to be more random than balloons would be, although I have seen some amazing sky displays from mylar balloons at sunset. A bunch of them still bundled together catching the sunlight as they twist around are spectacular.
The steady wind-related drift of such objects, usually in one direction, is a giveaway.
In my youth, Skyhook balloons used to generate a lot of sightings.