Well done Aaron; I'm glad you are enjoying this as much as I.
I've tried local sign shops and have not been able to secure any deals anywhere near as good as reported by some on here. They want huge minimum orders and certainly the prices are not good. Guess it's just election signs for me. Oftentimes the campaigns are pretty quick to clean up. This year the polls closed at 8 p.m., at about 11 p.m. I went on the hunt. Actually I was out scavenging until 2 a.m.
Some campaigns print right on the signs that they want them back for re-use; the sign shops can cut the 4 x 8's down to smaller sizes and print on them again. Many signs say no such thing. If I don't like the guy, I'll keep his dang sign regardless. I just won't drive around with any mods made with that sign where the name is clearly legible- throw some paint on it or whatever.
Re: Holes and rust: Holes get drilled there all the time when people install mudflaps and such; it appears to me that on the rusty cars, the rust didn't necessarily start at the holes. Plus, being in N. Cal, I don't imagine they salt the roads all that much, although you might get exposure to salty sea air? Regardless, I'm on the same page re: doing a little rust prevention there; I'd say if you're running sheet metal screws then painting the holes won't help much as the screws will expose bare metal again. However if you are using pop-rivets or something else that won't scratch the paint in/around the hole then perhaps some paint applied after the holes are drilled couldn't hurt.
I doubt you've seen leather over grilles; "car bras" are vinyl as far as I know and they are for protecting the front end paint from chips. One guy I know used a car bra to conceal his awful bodywork "repair" on the front of his car.
The factories have long employed straight air dams for the simple reason that they "hinge" when hit and thus survive the hit, vs. curved ones which inevitably break. Sure, for styling and aero purposes I like the curved ones and can't help but think they work a skosh better, but then I like the straight ones because they can take a hit and not need replacement.
I can't imagine a clear air dam looking good (dirty all the time, highly visible scratches) or surviving much of a hit but I suppose one could be made of that heavy, flexy clear vinyl of the sort you see in commercial/industrial warehouse/production/shipping doorways to control heat loss.