It's just all going to come down to opinion really to if you're going to get the full value out of this pack. Can play the waiting game and wait for a sale on EP's for it to be half off or if you're in the US chances are Target has it on sale already. I'm always for sales for sure. I have been enjoying this pack though I do have a good couple of disappointments in what they could have added to it to enrich it further.
List of things of note
Aqua zips (jet ski's)
Sailing (with canoes)
Swimming in the ocean
Building Sandcastles (when it rains they fall apart)
Suntanning/sunburns
Snorkeling
Diving (rabbit hole you can buy items from the booey to collect shells and take underwater pictures)
Freediving (about like the above, except your sim will come up for air now and again and don't need to buy anything and you may collect items)
Search the beach for shells and other items along with cleaning up trash on the beach
Shark Death (or it's suppose to be a shark that pulls your under)
A lot of new CAS items (more so for adults children get a little something but that's about the norm)
Different events that happen in the community part of the island (they pop up without notification)
New recipes
New drinks
New traits (child of the ocean, child of the island)
New Aspiration
BBQ pit ( that's on a timer letting the food cook for almost 2 sim hours )
Kava Bowl (this is replaced by the atrocious fruitcake here in this world with the welcome wagon. Sims get some buffs from drinking it and especially after they sleep. They can also get dazed from it)
New harvestables (Kava, pineapple, coconut)
Playing and befriending dolphin's (they can also fetch you items now and again if they feel like it or might come back empty handed)
Mermaids (Not as in-depth as vampires, but a big step up from the ones in S3. Can customize them and they are not invasive in your game unless you play a mermaid in your household or befriend one so you won't see them otherwise.)
Monsoons (if you have seasons combination of heavy winds, rain and thunderstorms)
Waterfall (Can woohoo it, shower in your clothes and shower in the nude, attract frogs to catch them as well as play in it)
Volcanic lot trait
New part-time jobs
Conservationist Career (pretty indepth and really useful when you get to the environmentalist branch which can effect the world around your sims by passing policies. Etc. No fishing after certain times, turning their power off after midnight. etc, etc)
Anti-environmentalist (sims that pop up with a red exclamation above their head they're most likely littering or fishing for poor baby turtles. You can confront them if successful you get a reward in the form of money)
So, if any of that interests you greatly I'd say go for it or just wait off for a sale for the most part as I'm sure it won't be long when they do. Also, you won't see other sims showing up in Sulani at all from other world's unless you have certain lots they'll flock to (like a restaurant or gym) So, you'll see a lot of locals and some sulani homeless townies.
What's of value to you might not be the same for someone else, so it's a toss up.
Would consider looking at Carl's Sims 4 guide videos opposed to a review from anyone as he goes into depth with different aspects in packs from skills to careers, etc.