So, what do we think some annexes would do?
Stables: Local horses for the palace, encouraging people to have stables in their areas so a local contingent of light cavalry is more likely, a dedicated courier service.
Gardens: Better health in fresh produce for the palace (leader longevity rolls? is that what the first one did, because I don't think we saw a mechanical benefit for it), pioneering gardening and encouraging local houses to plant their own gardens, increased effectiveness of diplomacy actions as they are impressed by our gardens.
Library: National Library, beginnings of places that have their own little libraries to run things more efficiently
Grand Hall: Area in palace dedicated to receiving different kinds of visitors (Likely would be very strong with a library upgrade in addition), place to showcase various ideas to visitors.
Thoughts? I really do want more annexes.