I believe that the additives do contribute to a healthy substrate system. Actually before I discovered ADA Nature Aquarium, I had done prior research on soil, agriculture and the like, which taught me the importance of building healthy soil to keep growing plants. So this concept was not unusual to me when I got into planted aquariums. I also examined the ADA literature closely about exactly what each product does, compared other products and also people who use these products and what they thought.
Powersand- This is used for those who plan to keep the layout a long period and also those who plant plants that like extra nutrients like Crypts and Downoi. An extra punch of fertilizer for the substrate like long term root tabs basically.
Bacter 100- Contains over 100 types of substrate bacteria. These help establish the tank with beneficial bacteria . Shrimpers also report good success when using this and other products I find. Bacteria in a bottle does work.
Clear Super- Food for the bacteria, pretty simple, , they need something to feed on, some do not use this though.
Tourmaline BC- This is Bamboo Charcoal, which has many benefits as a water purifier, etc, shrimpers often use logs of this as well, so I think it is beneficial as well.
Penac P and W - They help prevent the substrate from turning anaerobic and also help rapidly oxygenate the water at start up. If you gass your fish you can pour some to save them as they add oxygen rapidly to the water. These results are visible.
There is also Bacter Crystal, Boost P and Balance from Borneo Wild which are similar products and a little cheaper.
In the end it comes down to giving your planted tank the best start and chance from Day 1. I would also recommend Green Bacter (build good bacteria ) at water changes, Green Gain (good for plants) and ECA (easy Iron supplement).