What are the effects of upgrading the Mayor's Mansion?

I have plopped the Mayor's Mansion, and for every 4 or 5 hours of in-game time that I maintain an approval rating of 75% or higher, I am prompted to upgrade it. Since it is free to do so, I oblige. However, what is the benefit of this? Does it increase land value even further each time I click? All that seems to be happening is a firework show.

I did some more in-depth observations last night, and here is what I found:

• Each time the Mayor's Mansion is available for an upgrade, that means you have crossed an approval rating thresh-hold, and your sims wish to give you a gift.
• The gifts take the form of add-ons to your mansion, each which costs a little extra upkeep each hour to plop (about $10), but slightly increases the land value around the mansion even further.
• Each add-on is slightly more difficult to obtain than the last, meaning you'll need to hold a certain approval rating for longer, or simply achieve an even higher approval rating.
• Gifts include the following structures: Flag of the City, Mayor's BBQ Pit Patio, Circular Fountain, Mayor's Statue, Balcony, Guest House, Guard Post, Street Car Garage, Extension Wing, Limo Garage, Greenhouse, Tennis Court, Swimming Pool, Lookout Tower, Party Wing, Simcopter One.

According to the IGN guide, it "dramatically increases nearby land value."