Actually I was evil enough to test nature shrines in an earlier game so that I know (no they don't both work but you don't get a warning either). However there is a cheat ( I notified Twingalaxies and Malfadore about this already though
). System Robotoid facilities and Time shrines do stack even though they say they don't. You don't see it on the planetary resource screen (because all system adds are shown on the Empire screen) but if you build both and scrap the time shrines your production goes down. Maybe other overlapping system facilities also do this but I haven't tested any others yet.
[This message has been edited by Tomgs (edited 08 February 2001).]