Plastic Rubber
I've seen some better products posted before, especially for use on the type of plastic used for the wiper cowl panel, but I don't recall the name. Perhaps someone else can provide this.
The wiper arms specifically would need to be repainted though. They are not plastic, unless you're just referring to the plastic cover that goes over the mounting nut at the base. But the rest of the arm is metal and the paint tends to fade because folks rarely think to keep it waxed.
I always use 303 Aerospace to protect the various vinyl/plastic/rubber trim components across the entire car. It does a great job of protecting/maintaining pieces that are already in good condition (application should be done anywhere from once per year to once per month, depending on exposure/conditions), but it won't do much to restore pieces that are already sun damaged/heavily faded. I don't know if that product I mentioned above for the wiper cowl panel will work to restore the more flexible surfaces (such as the T-top trim, etc.) because I've never used it but, again, perhaps someone else can provide more info.
I'm with RPM on the wiper arms. They are not that difficult to remove. Kill an afternoon and re spray them with some satin black. Do have a wiper arm puller or your not getting the arms off. The pullers are cheap and it makes the job easy.

The original finish on these was actually pretty close to a semi-gloss, though they would quickly fade to a low gloss or satin look when not maintained with wax from new. Repainting is going to be the best option once these are significantly faded, as the paint is so thin that trying to restore the finish will likely not produce satisfactory results.
Im gonna walk back my comments to the OP. After further thought, since the fading/damage is done and any product you put on it will eventually wear away from car washing and rain ect. I would just buy the cheapest thing, and given the situation that were improving the appearance to a damaged part, a silicone based product like Armor All would last longer than the water/natural oil based products mentioned above.












