As for whether or not a weathering effect is historically accurate, that is very subjective, because a great deal of that depends on the age of the aircraft being modeled, maintenance activities/part replacement, and the environment it has been in.
Hi Eaglecash867, I completely agree, weathering is subjective. When I look at photos there is usually a wide variation from brand new to completely dirty and worn. It is easy for me to imagine circumstances when the ground crew has plenty of time to clean and polish the planes to look almost brand new. But there are probably wartime circumstances when the operational pace and manpower shortages mean the crew barely has time to keep the planes flying, let alone keep them clean. So historical accuracy often depends on which photo you happen to choose. And even If there is no photo, who's to say a model is accurate or not? At the end of the day, all planes are machines with fuel, lubricants, fluids, heat, dirt, exposure to sunlight, rain, etc. And will get dirty if not cleaned and polished regularly.
As far as panel lines go, in my mind the photographic evidence clearly shows panel lines in most instances. How these are portrayed on a model is a matter of personal preference. Imo these would be left off if trying to portray a brand new plane fresh from the factory. Wartime birds seeing heavy use with an overworked crew would probably have visible panel lines with varying amounts of shading. Along with other types of stains, grime, etc.
I love the photo of the RF-4C exhaust. I think the kit manufacturers can do a better job of molding these details into the exhaust parts.