Metal vs "plastic" buttons

The general idea with modded AC pads is just raise the sensor out of the housing slightly (if it's too deep - this is the case on old PIU SD pads) and to add more material to the top of the L brackets between the sensors and the panels. A big reason AC pads play well is that the panels don't have any give - they may require a fair bit of force to activate (especially unmodded) but the travel distance is very small. Every home pad I'm aware of besides the Blueshark is based on panels that flex to touch contacts together, instead of rigid panels that compress sensors. Nobody touches the insides of the sensors unless they've become over-sensitive.

There is no foam whatsoever involved in the sensors - they're metal contacts in rubber housings (separated by a rubber wall) and the things last a ridiculously long time. Most of my ~'99 PIU SD sensors are still in working order, although I have largely replaced the sensors in my pads with newer ones because they're more sensitive. The only foam in the design is on top of the L brackets over the sensors, and for decent performance you want to use as rigid of a material as possible. They're also not high maintenance, it's just a good idea to vacuum out the panels once a year and every now and then if you're really into it adjust your panel heights. Cracking those panels is also quite the feat, I've yet to ever see it actually happen even on really old machines, only heard rumors that it's happened. Thick acrylic is amazingly tough.

And yes, there are four per arrow. One on every edge.

Rubber would be awesome, I'm only somewhat familiar with the DDR AC pads, they are modded by replacing the actual foam, the foam itself in the arcade panels wears out. Arcade pads do give, the travel distance is the distance it takes for the sensor to touch and stop. In our Omega dance pads the travel distance is 1/8", in Cobalt Flux pads the travel distance could be much larger because the sheet metal had to be bent up otherwise it wouldn't even work and penny modding those pads decreased the distance at the expense of getting penny shaped indentations in the sheet metal. We use 1/16" lexan because unlike acryllic lexan will not ever crack but it is way more expensive, especially when you buy them in larger sheets rather than small panels. A thicker acryllic will last longer but it will eventually crack, that is the nature of the material and that's why those panels are commonly sold as replacement parts.