I would also like to suggest that along with galactic wonders, a new category be included; regional wonders. Some could be generic, meaning any species could build them. Others might be species specific - only the specific species could build them.
You are going to have be more specific about what you mean by regional wonders. In GC2 there were several types of buildings for planets. There were normal projects, the buildings you could build any number of times, ex. Xeno Farm, Trade Center, etc.; unique projects, you could only build one per planet, ex. Starport, Recruiting Center, Space Cannon, etc.; super projects, only one per civilization, ex. the various capitals, Orbital Command Center, Super Spy Training Center; galactic achievement, only one could be build in the entire game, ex. the alignment temples, Restaurant of Eternity, Gaia Vortex, etc.; and trade goods, like galactic achievement only after being built they gave you a product you had a monopoly on, ex. Aphrodisiac, Nano Recorders, Hyper Computers, etc.