But from a traffic and pedestrian safety perspective, i think it will just take a few nasty accidents for insurance and legal issue to spoil the fun. I can see the authorities demanding insurance coverage and safety management plans that would kill off most displays.
Ive had good luck with exterior grade polyurethane varnish diluted with turps. I also use clear spray enamel this year to stop my clear sets degrading in the sun.
Problem i found with the bigw lights ftom last year is that the clear plastic insulation on the icicle lights is not uv stable. Mine when dark brown after 6 weeks. The kmart lights are very fragile ive never seen copper wire that thin before, perhaps 5 strands thinner than hair...