Just wanted to bump this. I made the 'Parabolic dish' thing in the OP. I didn't use it for my router. I placed it on my PCI card's external antennae. It didn't really work at all.

Maybe the signal was too far or too weak (was trying to hijack neighbor's net) but I noticed no change whatsoever with or without the thing. I placed the antennae in just about every combination of directions possible and didn't get any improvement.

Took me pretty long to make the dumb thing too, Felt like I got scammed by a household hacker youtube video