What should I buy from the store?

To go on on what @Paikallinen already said. I'm just going to quote myself.

"SimLibby;c-17567461" wrote:

Sunlit Tides (standard edition) is on sale once:

• 972 ) Sunlit Tides / 1127 / 2450 / 54% / 2 hrs
  

If you buy Serenity Retreat as Daily Deal (DD) as well, you basically get the gold edition much cheaper:

• 100 ) Serenity Retreat / 1026 / 1539 / 33% / 2 hrs
  
• 244 ) Serenity Retreat / 589 / 1539 / 62% / 2 hrs
  
• 643 ) Serenity Retreat / 741 / 1539 / 52% / 2 hrs
  
• 690 ) Serenity Retreat / 513 / 1539 / 67% / 2 hrs
  

See also this post from angeljess26 regarding getting Sunlit Tides Gold much cheaper. The cheapest you can get it for is 1640 simpoints. In this post by Me1620 you will find personalized Time Zone Specific DD Trackers Spreadsheets so you know which date you can expect which item on the DD.

I have Sunlit Tides. It is a beautiful world and it plays really nice. So have fun with it when you (eventually) buy it. :smiley:

The list rotates so you will get another chance to buy Serenity Retreat.

"Me1620;d-866448" wrote:
The current Daily Deal list, which was introduced on September 23, 2014 at 12:07 a.m. UTC, includes 977 deals. After the 977th deal ends, the deals begin at Deal 1 again. A full rotation of the list takes 82 days. (See this post for background information about the Daily Deal list.)

EDIT:
Anyway, I think you should keep an eye on the Daily Deal Rotation List for good deals (including venues). It will save you lots of SimPoints. I have most venues for a fraction of their regular pricing. You can unhide all the spoilers to see the DD's. Use + to search quickly for the items you're looking for (just make sure you unhide all spoilers first before you start a search).
https://forums.thesims.com/en_US/discussion/866448/daily-deal-dd-2018-rotation-list-and-sales-help/p1