Thank you, everyone, for such insightful responses! @csboling, that’s the exact spot in the video I was referring to, though, the more I think of it, the more I could do such simple geometric overlays using Flash or something else software-based – and maybe what I want is something a little more messy. And, as you put it, maybe what’s best for my first video synth is something that encourages me to play around, experiment, generate some chaos, and, y’know, learn. Plus I have seem some things done on the Vidiot that are more or less exactly what I had in mind – particularly bits of this video – and if this example is some very masterful wrangling of the Vidiot, then there’s something to aim for, right? 
@Dewb –– good point. Maybe the question is to figure out which would be a good starting point, since I could easily swap my Vidiot for a Visual Cortex or what have you later on?
I very much want to make blurry, hazy video paintings; they don’t necessarily have to stand still, or necessarily be symmetrical. Some kind of dancing, breathing “aura” is what I’m after. I think what it is, is that I want to be able to simplify at least one of the variables at play (i.e., it’s a moving pattern but it’s just moving in one direction, not a hundred at once) and control the mess a little bit.
Right now I’m leaning towards Vidiot, with the sense that it would be a great intro to video synthesis, and that it would give me more variables to play with right off the beginning – I would rather not get sucked immediately into a video version of audio modular synth G.A.S., and could see the Visual Cortex being very dangerous in that regard. 
