I've switched to Nelson water based polyurethane paints, primarily due to the toxicity issue and not having the proper equipment to use the two part auot paints properly. The Nelson clear dries overnight to a hard clear surface. Adhesion with glass, epoxy primer or nelson colors is really excellent. You could ask Gerry Nelson (Jerry?) whether it works over Omni - I suspect it will. The one thing it does not stick to is automotive spray can lacquer primer.

I've had good results with this stuff. Application is a little different since it takes about 5 thin coats for coverage on the colors. The first coat looks REALLY bad and you wonder what you did wrong. But the second looks semi-OK then the third - fifth looks great and you are just building coverage. It's probably not as good as omni but I haven't yet spent the elbow grease to sand and buff it. Just out of the spray gun onto the plane you get a pretty decent result. No waiting a week for it to maybe get hard as with the Ultracoat stuff either, the next morning it is hard enough to handle then after a day or two it is hard as a rock.