>would the effect be lessened by substituting conductables for composites,
No. Composites are better as they do not contribute to the problem.
For example, you will not find stray voltage from a plastic water cup to the floor or from a dry wooden gate to a concrete wall.
>and running all on 220V?
If the stray voltage is coming from something bad like cracked, wet insulation on a wire, then 220 V won't help.
But if the problem is from neutral current, then obviously using 220 greatly reduces the neutral current.
