Some great news. I fixed it! Well, I greatly improved it at least.
So, it wasn't the marquee or anything like that. Very simply, one of the wires in the bundle with RGBH&V feeding from the JAMMA into the monitor chassis needed to be reseated and/or replaced.
I diagnosed it by carefully moving some wires around while my wife watched the screen. We noticed that when I moved the RGBEVH bundle the pattern would change, decrease or increase. So, I powered everything down, unseated the bundle from the monitor chassis, kinda straightened the connectors a little, and plugged it back in. Turned the cab back on, switched to a game on my Arpicade (Journey, blue screen) where you could see the pattern easily and it was GONE! =)
Now, having said that, after moving the cab back to its usual spot, when I looked at the color test display again the sparklies were still there, but much less pronounced. Basically I determined the white wire going into H (horizontal sync I guess) is a bit wonky. Even some minor movement when I moved the cab caused it to shift just enough to bring back the issue a little. So, at some point I will try replacing that one wire, which I think will fix the issue for good.
For now, I have it placed pretty well and see virtually zero sparklies or weird pattern noise as I did before.
Anyway, maybe someday this info will help someone else with a similar anomaly.