The two major changes to my original design were 1) using laminating sheets instead of packing tape and 2) using a retroreflective sheet for a liner material.
The laminating sheets are slightly thicker and much, much more tear-proof than packing tape. They're also much larger, which meant that I could connect big pieces together with glossy, unbroken surfaces.
The retroreflective sheet is something I've used in other instructables. What is it? I wrote it up in this instructable
(which also has some good tips on where to find it on other steps and in the comments).
Why did I use it on my wallet? First of all, it looks awesome. Because of the way it interacts with the light, there's a subtle shifting to its highlights. The photos don't really capture this. I used a black tape, which glows white in a camera flash or headlights. I faced the backing out, which produced a much more subtle contrast with the circuits on the keyboard sheets. I could have also faced the black side out, which looked even more awesome in some ways, but the contrast in that case was a bit too flashy for me.
The other reason to use this retroreflective sheeting is that it's foil-backed, which means that it will provide some protection for any cards in my wallet with RFID chips. Other good options here might include plain foil or antistatic bag material, both of which could look pretty cool, too.
See the photos below to see what the materials I used look like.