I assume when the Fine Paints people think of a roller they are thinking of a thick-knap roller as used to paint walls and ceilings. I would think you could get a smoother application than a brush with the high-density foam (ultra-smooth finish) rollers we are talking about in this thread, especially if the paint self-levels.
I'd also be interested in how much they recommend thinning the Ducalac with their mineral spirits for rolling.
All told the Fine Paints primer and paint system plus their mineral spirits would put you around $200. That's still cheap compared to getting your car painted, but you could probably by automative paint to roll on for those kind of dollars.
I think the Fine Paints system is interesting if we could adapt them to this method. On the website you can order a free small container of the paint; might be worth doing to try some experimentation.