Arch,
I agree with you regarding water based paint for several reasons. One big plus is that the water based clear will not yellow over time. I've never found a polyurethane that didn't yellow over a white base. Two or three part auto clears are good, but expensive, dangerous to the lungs, and hard to clean up. Nelson's paints are water based as are Warbird Colors. Their clears will never yellow. But...I've never tried to color sand and polish water based clear. I've heard it doesn't work well. But for sport flying, I like the water based products.
Paul