If I may butt in briefly, one of the concerns I’m having lays in the definitions being considered. Using spam in order to increase claim area is obviously against most people’s idea of fairness. But, what is the definition of spam? And is FC’s definition fair to players?
In this example of yard lighting using only 11 torches, I would claim that this is not spam at all and it is unfair to the player to call it that. These CE maps are beautiful and at night they are often too dark. Don’t change it - it makes the game more fun - but within 10 or 20 block’s distance from our bases such lighting enhances our experience of the game dramatically.
Likewise, a road often traveled and/or in immediate view from our bases will benefit dramatically from 8 or 10 torches and also may fall more into he category of “public works” rather than spam. Considering FC’s resolutions include account suspension 
, these definitions of spam likely won’t be acceptable to a lot of players.
In neither case did it appear the players were attempting to increase claim area by spamming placeables.
The reason pillars are often used with standing torches stems from a lack of understanding about how the build system’s decay works. So instead of building foundations out to the desired position of the torch - placing the torch - and then removing the foundations thereby tying the torch’s decay to the base, players add a pillar thinking it will increase the amount of time the torch has before it disappears.
A possible solution here might be to remove the falloffs toward claim borders. So, within the claim borders defined by foundation groups (not designated as “public land” as per your proposed solution), lights, benches, containers, and etc. all inherit a common shared decay time. Such a solution might also reduce the computational resources imposed on the servers. “1” usually requires less computation than “100” divided by distance.
Allow some of my recent photography to serve as RL examples:
