So I've got some background in electrical. I worked for a battery charger company for a little over half a decade. They used both copper and aluminum wiring, and in my experience aluminum is approximately two-thirds as conductive as copper is.
Trying to see if how feasible doing wiring via a flat sheet is. Typically the thickest wiring you'll see in a pinball machine is 18AWG, which has a stranded diameter of .048", or or an area of .0018". If I want to run with aluminum, I need about .0030". If I use .012" thick alum. foil, I can achieve 18AWG conductance at only 1/4" width traces (for high amp), and although 1/8" width is probably overkill for low power and signal, I don't know that I'd want to go much narrower than that.
I can buy a .012" x 20" wide x 5 foot sheet of aluminum off Mcmaster for just $19 which is not bad at all. I could probably cut it myself with scissors, but I may just have it waterjetted depending on how complicated my electrical layout gets.