Fine drawing, Marco. Mighty impressive.
No, not everyone needs an optical device (I won't say "aid") but some may wish to use one for a variety of reasons, not the least of which is that not everyone has your skills. But there are other reasons, too.
Dürer wasn't just drawing, but analyzing perspective to better understand how it works. You no doubt have noticed that in some of the Dürer examples, the eye is positioned well above the center of the grid, giving the same effect as dropping the front on a view camera. When researching this stuff for an article I wrote for
Pinhole Journal - holy cow, 20 years ago! - I encountered a lot of really interesting stuff. Euclid understood linear perspective, for example, but was uncertain just
where in the eye the locus of perspective would be.
The intersector is a great tool for understanding how perspective works. When I taught the view camera I had the students make pinholes and an intersector which they attached to the front standard of the camera, and a stick on the rear standard to locate the eye. Then, I asked them to take an object to place in the foreground of a scene, and using three bellows extensions (short, medium, and long) to photograph that object and scene rendering the foreground object at the same size in each image. This required moving the camera back or forward, away from the object or toward it. The resulting images clearly showed how the relationship of the foreground to the background changes. This is frequently fairly difficult for students to understand, and this exercise was very helpful for them. Also, the employment of the device is useful in understanding the Scheimpflug principle.
These days, some very interesting work is being done using perspective. Gillian Brown has been painting from photographs right on the location where the original photographs were made:
http://www.gillianbrown.com/JillStairs-1.htm. These works must be viewed from a particular point to make any sense at all. There was a wonderful example of her work at RIT in the office shared by Jeff Weiss and Elliot Rubenstein. She had made a hole in the door, and projected an image of Jeff in his chair, looking at the door, right across the desk, the wall, and everything. Inside the office, it broke into confusing patterns, but looking at it through the hole in the door it was astonishing, just like he was sitting there looking at you. I don't know whether it is still there; I guess Jeff has moved on. Eric Renner is also making perspective boxes. He has a chapter in his book about works of this kind. I find this stuff a lot of fun.