Is true, I have tested it and no additional bonus when used on self.

just another prank for dragon shamans as always ...

The additional bonus should be a higher % of the skill effect on yourself than other people.
So it means if you give to other +20%, on you will receive something more.

It has been discussed and these additional bonuses will be increased with the next game version.

So for example, if Dragon's Aid gives 20% to other people, a Dragon Shaman will receive 40% or more?

Not another dragon shaman; yourself will receive something more.
I said something more because I don't know and checked already the amount of plus bonus it gives; when it will be increased I'll check them
But i think sadly before it gave just 1-2% more; let's see with the changes.