What I noticed at first was that we have copper cables with aluminum crimped ends bolted to aluminum with a steel bolt (electrolysis). [/quote
Congratulations on the purchase of your 2005. It's nice to see so many Insight owners purchasing a second or even a third car. It says a lot about the car and owner loyalty.
FWIW, major automotive manufactures use ferrous bolts and fasteners electroplated with a tin-zinc alloy to prevent corrosion whenever fastening parts to an aluminum body panel, casting, or forging. The tin-zinc alloy offers excellent corrosion resistance in this appliction. The electroplated bolts are also dipped in what is known as a chromate solution that gives them a dull yellowish brown or yellowish green appearance.
Years ago ferrous bolts and other fasteners were plated with cadmium to achieve corrosion resistance whenever attaching a ferrous fastener to aluminum. By the 1970's cadmium was considered somewhat toxic (not so much to the end user, but to the environment in general) and other electroplated finishes were developed to replace cadmium whenever possible. For automotive applications the tin-zinc alloy has won out. FWIW the aircraft industry still uses cadmium in most aluminum joining applications.
In some ways the tin-zinc alloy is superior to cadmium in that it is ductile, a good electrical conductor, and easily solderable. For a threaded aluminum electrical connection (such as the Insight ground strap) it is often the practice to make the bolt/insert clearances tight. This allows the electroplated bolt to "scrape" the female aluminum threads on the way in, thereby removing any aluminum oxide (which is a very poor electrical conductor) from the electrical connection. The ductile tin-zinc alloy fully "fills" the threads and in doing so prevents further oxidation of the aluminum and hopefully assuring good electrical conductivity. However the tight fit also makes it harder to remove the bolt, but not normally as difficult as you described.
If your bolt had any corrosion on it, I would reccomend taking the Insight in on warranty and ask to have the bolt replaced. Have fun with your new car.