Contributer level decay?

Yes, your CV Level will drop over time due to games being added to the bundle list, as well as price drops in the Steam Store.

When the price for the game(s) you gifted drops (because regular pricedrop or because of bundels) so will your contribution level.
I am sure it's in the FAQ somewhere or somewhere else. I have read it somewhere :)

In the FAQ: "What are levels, and how can I increase my level?" #3 covers it pretty much I think?

Thanks for the replies, I must have overlooked that