Warning: considerable amounts of rambling ahead, along with some clean sections
Places of Power are built, then activated with a Necronomicon. The implementation is complete (could possibly add some additional bonus to things in the area at some point), with the lacking areas being the amount of structures to build, and unlocking them.

An idea that has existed since the thought of Places of Power is additional decorative blocks which would be used specifically for these structures. Those blocks could be gated behind anything, and would likely produce more efficient structures.

Making use of the knowledge system is also something that should be done fairly soon, primarily to have the player at least delve a bit into generating PE before they can do it without any consequences (who's to say the player automatically knows how to "properly" utilize statues without any trial and error). Broken versions of the structures could generate throughout the world, where the player could inspect the structure, and by doing so learn how to create that specific structure.

Things to do

• add decorative blocks to use as part of the structures
• maybe implement the means of adding an additional bonus to things around the structure
• incorporate the knowledge system, requiring the player to unlock the feature
• add ruined structures generating throughout the world that players can inspect in order to "learn" how to build that particular place of power

As with any issue tagged with development, any input and/or feedback is appreciated, or you could just bitch about it on Reddit (and I might come across it at some point in time).