If you had a marginal spark, then the copper core wires would transmit that spark better to the plugs without any loss...It seems you have plenty of reserve battery to run the coil, and you aren't going to see the low cranking voltages of a 6 volt system in poor shape. I wouldn't change a thing, your neighbors still listening to AM radio will thank you.
I've replaced lots of wires on old tractors and jeeps and usually all the local parts stores have in stock is a carbon core set. Copper core sets are hard to find unless you mail order or special order in anyhow. So most jeeps eventually end up with carbon core wires.
By the way.....if it takes as an example, 10KV to make a spark jump the gap at your spark plug, guess what the spark voltage will be with super duper wires, an incredible coil, and the latest, greatest, superzapper distributor, painted screaming yellow with chrome trim?
Yup, still 10K volts. You won't get any hotter a spark under the same conditions. (This is simplifying it a little, admittedly. ) Where all the HI Perf stuff shines is in unusual conditions, like wide open throttle with high compression, etc. Your low budget system may not be able to make the spark jump the gaps reliably under the more extreme pressures, etc. But, unless you have a Supersonic head shaved to the minimum, pop up pistons, and are running avgas, while towing houses around, you won't need all that.
