Kyle,
Both of your ideas are pretty good.
Bosch markets their European truck horns as a “Starktonhorn” (in England they label them “Supertone Horns”). They’re 15 cm round horns that sound like our beepers on steroids. They’re tuned e-g (390 Hz – 490 Hz), I believe. I had some on two of my earlier VWs. You must use a relay. They will be taken seriously. If you can’t find some on eBay or elsewhere, I would recommend hunting down a pair of good Bosch horns as used on larger Mercedes Benz models and some Volvos in the 1970s and 1980s. Check out local foreign-car junk yards, if you have some. Whatever you end up with, you’ll want to fabricate some nice-looking brackets setting them above or below your front bumper. Look at the various photos on the Facebook page “Copbug Polizeikäfer” to get an idea what they should look like. But if you want to hide them (and muffle them a bit), you can also weld in a horn bracket underneath the right front fender and mount one of them there, wired in parallel with its mate on the other side. Use a relay!
There are lots of authentic German backup lights (SWF, Jokon, Bosch and Hella all make them). You don’t need to drill any holes in your sheet metal, as the brackets bolt onto or through your bumper brackets. Even a Bosch or Hella clear fog light (use a relay) can do a good job. A back-up alarm is fine as a pedestrian warning, but obviously does nothing for your visibility – or vision. Lights are always useful.
Did it help? It depends on what you use your horn for. If it’s intended to punish, then yes – it helps. If you just want something different – yes, it helps. Does it prevent collisions? Who knows? Since I back down a long, dark driveway, the extra lumens of a backup light most definitely help.
Bert