Personally, I never bought any of the skins. I wasn't a fan of missing out on them, since they did look nice, but it's a simple concept of me not wanting to spend extra money.
That being said, I completely understand why you were doing it. What I don't understand is why people were upset about them. It could be said that releasing exclusive content before the game is completed seems like it's a money-grab, but clearly it's not. You are providing us with continuous updates, you clearly listen to the community, and the skins did not change the game mechanics or story at all.
It's obvious that the skins were a way to raise funds to keep developing the game. The fans who want to support you and could afford doing so would get rewarded for it. The people who couldn't afford it wouldn't get anything. It's as simple as that. Some people are either just entitled or sensitive and can't comprehend the concept of investing into something and getting rewarded.
Please don't take this matter to heart RNGeusEX. We love you and the game!