If Bitcoin network fees get higher than shipping costs, it would make sense to start giving participants physical goods for their signature campaign participation. I think it would be cool and probably help cut down on abuse if people had to give their mailing address to be a part of the campaign. Maybe try shipping some silver?
I doubt that giving mailing address is a viable solution to stop abuse because anyone can use drop shipping services or their relatives address to receive the package for them. Using altcoins is still more convenient solution rather than using a physical rewards that will take more days or months to receive depending on the type of courier the sender will use.
Services on Bitcoin or Altcoin doesn’t matter anymore because campaign participants will surely always follow the campaign whatever the location. Even bounty section on altcoins is once become popular when bounty campaign pays high during the 2017 hype.