Personal preference, with all the factors mentioned above. Good responses all. I'll add a couple. Paint it and it will change your attitude to the car, not always for the better. How much more money did I put into it (and will I need to get that out of it some day?). Never bothered me when I had a car painted, but some guys think their car's made of sugar after that and it'll melt in the rain so that changes how you use the car a little. I have a tendency to pick out the flaws in the body AFTER it's painted, no before, so unless the paint's perfect, there's that.
Patina is no more a fad than preserving anything that's old, like a painting, a coin, a sculpture. It has more to do with what you want to show in the car. I've restored a Nova, and loved the way it looked, and sucked it up on the cost of body and paint. It was the right decision, and I thoroughly enjoyed that. But the car I have now is infinitely more interesting to me unpainted, as it has surface rust and original paint ONLY on the car, with no dings or dents. In some ways I like seeing a car like that more than one that's painted as there's no mystery about the body panels, rust or bondo. You get what you get.
And though there are some quality shops out there somewhere, no thieving, 5-hour a day, foot dragging, over-charging, parts-losing coach craft body shop will get a single dime out of the Chevy II I'm wrenching on today.