If you want long term evangelists you're going to have to think outside of the relationship between your product and the customer and focus specifically on the customer.
Identify the influencers who are already engaging your brand through social media channels and see what you can learn about them.
If their profile picture is them playing an instrument, you might send then a gift card to Itunes or Guitar Center.
In Short: Spend a little money and show your interest in them instead of just rewarding their interest in you.
I had Wheat Thins send me a box of crackers and that was cool but I sent one tweet out and was done. General Electric saw that I was wearing a Batman shirt and sent me a really cool book as well as a hand written thank you note.
I regularly engage and promote content about GE.