Hero Hunters VIP is a feature that lets you increase you power based on how much money you spend on the game. Things can get pretty expensive if you planning on getting to the highest VIP though you will have a much easier time with the more difficult areas of the game.
You can view the 15 different VIP levels and the bonuses that come with them by scrolling the VIP Benefits List to the side. Many of the benefit that you receive are daily bonuses that can help you out in different areas of the game. Some of the stuff you unlock will help you out when you spend real money on different things which isn’t that helpful and is more of a money making tactic. Each new level will include the bonuses from the previous levels so you will have a pretty good build up of extras.
Using the free gold options doesn’t seem to offer and VIP points as your going to have to spend real money to increase it.
By the time a person got to level 15 they would have spent a lot of money on the game purchasing gold and should have a decent team by then. This game seems to be gears for you to play for along time. So after you have reached maxed level you will probably have a lot of game left to play unless you have gotten pretty far before maxing out.
If your interested in more related information you can check out the Hero Hunters Wiki.