Block Count Limit Within Range
I believe that it would be really healthy to limit the number of copies of a single trap within a certain distance. While I know this would somewhat limit player creativity, it would also greatly reduce the number of low-effort bases that simply place as many plasma sentinels as they can.
Alternatively, greatly increase the threat of a trap once more than a specific number within a given range exist. (This may prove challenging, as I know that the threat calculation function is already running pretty long.)
Alternatively, greatly increase the threat of the Plasma Cloud mod. A flat increase that doubles their threat with this mod seems completely justified.
Alternatively, increase the cost of the Plasma Cloud mod. All high-end bases are using it excessively and that very much indicates a balance issue.