I was just wondering and I dont know if it would work, but you can get those cheap yagi antennas on ebay that are made out of solid aluminum. I read an article somewhere that the elements are parasitic except for the driver. So I was thinking about using some heat shrink wire insulation and drilling out the rivets to insulate the elements. Im not sure if it would but it might make it (more)directional.
No, it wouldn't work that way. If anything, it would make it less than directional.
You are correct that the director elements are parasitic, and they are attached to the grounded boom. Same as the reflector element. Many years ago I built my own VHF yagi for use on 2 meters. I used a length of PVC pipe for the boom, and while it didn't bond the reflector and director elements together, it still worked well.
Usually the way you make a Yagi more directional (tighter pattern) and better front to back ratio, is by adding more elements. Isolating elements from the grounded boom isn't going to help. What you'd want is more director elements.
Yagis can be really easy to build. I know some of the ones on line are cheap, and they may be a good source of materials, but you can brew your own pretty easily.