Well, nobody mentioned spiral wound high tension wire. I suppose because it was never very popular, but it help with rfi, yet does not have the issues carbon filled wires are known to exhibit.
The real key here is how hot is your spark? If you can pull an inch of spark, then carbon resistance wire should be fine. If you can only pull 1/2" of spark, you better either improve your ignition or stick with solid core wire. (NOTE, I did not say "solid wire", I said "solid core wire", which is the correct name for copper wire, either single or multiple stranded.). Carbon core resistance wire will eventually fail, quicker with high heat, but it should last an easy 20 years or more.
Just what I think I know...