Thanks Metro!
I actually managed to practice quite a bit for this one which was extremely helpful. In the test file I did each party at least once, making notes about what tasks were given and what the gold medal reward was. And then I spent a little time on checking out the townie houses and making more notes about what party related items they had (eg bars/games items/etc).
The most useful thing I discovered in practice was that the rewards for a gold incognito costume party is a lot more valuable than the rewards for any of the other party types (at least in my game). And by "a lot" I mean around 10x more valuable. So my strategy became very focused around fitting in as many incognito parties as possible.
Having less packs was actually an advantage for once, as I only have 7 different types of goaled parties. After including dates as well that meant I would have to start a new rotation of unique parties on day 9. So of course I organised things so that the incognito party is one of the days in the repeat rotation. And I don't have spooky or toddlers parties either, so once we got to the party hearty stage it was just non stop incognito parties.
Since I know that I often have issues with running out of time due to my snail like pace, I made the decision that on most of the non incognito party days we would only have one party to meet the requirement. That allowed me to then use speed 3 through until the next morning and meant I actually got to the party hearty stage.
On the first day my sims worked hard to prep before heading off to hold a keg party at the Zest house in the evening. Our prep involve building useful skills such as cooking and mixology, getting my two sims the always welcome reward trait, and packing both of my sims' personal inventories with everything I could think of that might come in handy. Eg. Portable stereos, portable bars, mysims dolls & flirty paintings (for their emotional auras), laptops (can count for games tasks), fruitcake (though we never ended up using that). Clubs were used quite frequently - to take care of needs with rally the troops, and also for meeting people.
I failed to get gold medals on five parties including 3 incognito parties which was annoying. Four of the failures were because of the "make coffee or tea" task. Apparently the game has no qualms about giving this as a party task in houses which don't have a tea or coffee maker. Either that or I'm blind, but I did have a good look for one when it happened. And unlike with dates, there is absolutely no leeway for error with a gold medal party - if you can't do 1 task, tough luck - no gold for you!
(The fifth fail was some kind of bug where mid party the game just stopped registering that tasks were being completed. I could have asked for a ruling on what to do but as it was late Sunday arvo here, I decided to just call that one a loss, ended it and got on with a new party.)
Some of the costumes sims chose were very much "what on earth were they thinking?" that I wish I'd bothered to take some photos. Like when one of my sims choose to wear the head piece from the hamburger costume on her head but not the rest of the costume, just the head piece with a regular summer dress.
Definitely 1/5 for effort there! Though I like how that makes it a bit more realistic - having some sims who have gone the whole hog in finding some elaborate costume alongside other sims who just grabbed some random stuff/a mask.
Happy to answer questions if there's anything further anyone wants to know.
