Little update. Before trying some new microswitches, I decided to give a try to the replacing method showed in that video on post #10.
First of all I removed that protection film that covers Nintendo contact plates, making them look of a grey colour.
Their diameter is littler than the original ones, but they have a good concave shape. I decided to replace all the directional stick contacts. As illustrated on some tutorials I lifted the platic ring that maintain in place the plastic activator. I removed it and got access to the contact plates. They had still a good shape, so I decided to save them for other pads. After removing each plate I scraped (very softly) each contact and cleaned them with a bit of alcohol. Then I put in place the nintendo plates and the plastic activator. After that, I lowered the plastic ring and with a soldering iron reinforced it. I lubrificate the pivot seat and the white plastic arrows in which springs play againts activators. Just to finish the project, i washed with cold water the joystick protection mask (that takes in place the four tactile microswitches) and the the two halves. Ok everything in place, closed the joypad and tested it. It really works well and those nice "clicks" got back again. So I think that if you have a joypad that needs a "medical attention" this could be a good option. Hope it helps...