Good luck! I mean that sincerely, not sarcastically.
I shall confess to having spent diamonds on the Summer Event. Not that I'm ashamed of it, there are a lot of good resources to be had which are very useful for small cities, like mine. Those with an Arc etc etc may poo poo the desire for such trivia as attack boosts, the Governor's Villa etc, but I think they probably forget what it was like when they were just starting out.
No one in their right mind will crap on boosts for the Attacking army... Defending army? Yeah that's pretty useless.
Gov's Villa was buffed massively from it's initial beta release, (ie: originally, there was 0 fp production), and that's easily shot it IMHO into the no.2 spot for "best event buildings of the year" for 2020:
1. Hoppodrome Carceres
3x4 that give 10% def boost to attacking armies + 6 fps to top it off. Even if you build nothing else for the chain set, this building is gold!
For just 2 tiles more than Gov's Villa, you can get both ends for added resources + 1x Rousioi Track for an additional 6% def boost to your attacking army.
2. Gov's Villa
Massive atk% boost and fps - need I say more? Troops are just a nice bonus, but there's far more efficient troop production via settlement rewards, so if you're building it for that, you're choosing the wrong option.
3. Olympic Treasury
Nice def% boost for attacking army + good fp/tile generation. Hippodrome though is stupidly better def%/tile however & it's fp/tile is also ever-so-slightly better too.
4. Mikawa Bridge
Very good fp/tile generation, but it's definitely an awkward one for early game cities due to it's size. No military boosts either, which definitely further adds to the lackluster appeal.
5. Celtic set & Airship
SKIP!!
Note that the difference between the top 3 slots is overall pretty close... Every one of those buildings is definite A-tier material, with Hippodrome pushing into the vaunted S-tier if you have the proper room to set it up. (ie: only Sentinel Towers are more OP in the def% department)
The latter 3 I would place in C-tier to outright garbage-tier for what they bring, or rather, what they don't bring.