Oasis Springs should have a pool. I say this so definitively because that place gets HOT in the summer and it has no pools anywhere because no pools in base game at launch.
Other ideas:
A board game cafe
An outdoor theater
You could have libraries and museums that are designated that way by default but set up to be art centers/schools or commercial office work spaces, or like an Internet cafe or a city hall.
A roller rink
A bowling alley (maybe some sort of Rec center)
A community center/shelter/motel that provides free beds and showers (for if you ever do a Rags to Riches challenge)
Community garden (which could even be like, you could have an orchard on one lot and just a flower garden on another - depends on how much you and your Sims like gardening)
A wedding venue (which could either be a religious building or a city hall or community center type building)
Restaurants if you have dine out
Spas using combo SE and SD
I’ll come back if I think of more.
ETA: not sure how your Elementary school operates but you could do a building (perhaps another school or this same one) where it’s set up with skill building for children and teens like a tutoring center or somewhere to go after school or on the weekends.
A music academy for learning the music related skills (and possibly dancing).
If you have fitness stuff you can do a gym specifically with a rock climbing wall area.
Perhaps Magnolia Promenade could have bars/restaurants.
DSV could have a nightclub or lounge.
Some form of retail like an electronics store or furniture store or a toy store.
Some sort of factory for skill building the handiness/woodworking skill and doing the Eco Lifestyle crafting stuff.
Vacation activity ideas is very tough for me to think of. Sulani can have the water activity stuff. When I have gone on vacation IRL, I go to restaurants and shop and go to historical sites or natural sites or museums or large shows at venues. I’m not really sure how to translate that into gameplay. I suppose you could add national parks and have activities for like the wellness skill, or pools that look like lakes/ponds, ways to obtain certain harvestables, etc.
Oh, maybe some sort of amphitheater or stage location for musical performances.
Maybe some sort of social club with the intention for Sims to gain Charisma skill.
(Basically I like to think of all of the skills that Sims can gain and how that can translate into gaining those skills on a community lot, that way you can make use of different kinds of community lots that also help your Sims, and you don’t have to fill their houses with all kinds of objects specifically for the skill).
Some sort of science museum for the rocket, for example, would be more fun to me than having a rocket on a residential lot.