How do you decide when a track needs more production elements versus when it's time to strip back and keep it simple?

It will depend always in the genre you are working. 

For example, If I make an acoustic cover I know that guitar + bass + piano will do. But if I work in a Deep House track I know I will need more sounds and fx to make it work. 

The genre always determines how complex the production will be. Orchestral music is another example of how you decide which way to go when it comes to the production. Do you need a brass section? Or is it enough with strings? 

The concept, vision and need for X project will be the most critical thing when it comes to decide how the production should be. 

It's similar to decorating a room. We add items until it feels just right, but if we keep going, it eventually starts to feel cluttered. We avoid piling too much together or using too many or too few contrasting elements. In the end, it all comes down to personal taste.

It’s about the vibe. If the track feels crowded or like it’s losing its groove, I’ll strip it back. Sometimes less is more. But if it feels too empty or lacking energy, I’ll add elements to fill it out. I just trust my ears—if it clicks, it clicks! Easy, right? 

If the message is lost or overshadowed by fancy production elements, then it's time to remove the distractions from the original message.  The same applies to both music production and commercial productions.  
For example, in TV commercial production, we balance the mix to the dialog first, then add in the music and fx beds.  If at a low volume, the music and fx beds are distracting or heard louder than the on camera dialog or VO selling the product, we rebalance, duck, or cut elements to make sure the message is clear. 

Having written and produced songs that has more than a billion streams, I think its a lot about feel. If in doubt reference tracks you like in the same genre and really try and understand what they did and why

From my personal experience of over 10 years in producing music, I would say that I definitely believe in "less is more".

You also need to think about who your audience is, as well as referencing similar professional tracks to yours. I find that once I show my song to some of my producer friends as well as to my non producer friends and none of them mention any feedback, that may be a good sign that the track is done.

Finally, I would mention that you should have a main element playing for each section of your track. Meaning that if when listening to it (helps to listen at low levels), you can clearly hear the main element you want to enhance, it's a good sign you are on the right path.

Don't forget music is quite personal, so follow your gut to and if you feel that adding small "ear candy" or tiny atmosphere details that even the average listener won't notice, feel free to do so too 

The best advice would be:
Don't look at what you can add, look at what you can take away! 

Goes for a lot of things in life actually.
 

Deciding whether to add more production elements or keep a track simple depends on the song’s core message and emotional impact. If the song feels like it needs more energy or depth, additional layers can enhance the arrangement. On the other hand, if the emotion or melody shines through on its own, stripping it back can create a more intimate, raw feel. I usually trust my instincts and listen to what the song is asking for—sometimes less is more, and sometimes adding a little extra brings it to life.