You then took that clicker to your local arcade, and clicked one of the corners of the CRT, that would send a shock through the system and add credits to your game. I believe this was because the CRT was grounded on the same ground lines that the mechanism for physically checking a coin had gone through the system.
Suffice to say, they caught onto this over time, and added some form of an alarm into it. But up until then... Those were truly the best times.
Those systems are occasionally used in bars in the US, though they've dropped the whole plate and it's usually just arms where the holes are.
To my understanding, at least in the US, they aren't used for deep-cleaning anything. That happens with soap and water in the back still. The upside-down-showers are used to clean out the dregs of someone's glass when they get a refill (you give them a glass, they give it a quick rinse, refill it and hand it back), and as a quick rinse for new glasses to clean up water stains/detergent residue and anything that might have fallen in since they were cleaned (hair, dust, etc).
Mileage obviously varies, but the "beer nerd/snob" bars I've been to simply don't re-use glasses without a full wash. They'd rather just charge a little more to hire more dishwashers and be able to absolutely guarantee that there's no leftover beer/water in your glass when they refill it, and that the glass is refrigerated if that's something they want.
I've always heard the head/foam had more to do with how you pour the beer (more impact/movement = more foam), but it makes sense that temperature affects it as well. There's some kind of official course on how to pour Guinness to get the correct head on it. I don't remember the whole thing, but it was something about holding the glass the correct distance from the tap and tilting it so that the beer "slides" down the side of the glass rather than a direct perpendicular impact with the beer already in the glass (which makes more foam).