Just received an email from Habbo (although only for one of my clones and not for my main acc :S) - but it says you get 1 point for every 1 credit you buy, and a bonus 120 loyalty points if you buy over 120 credits in a month, and they can be exchanged for rares, HC or even more credits. Will be interesting to see the price of each rare, and the amount of extra credits you could get.
Here's the email:
Earn Loyalty Points for every Credit you buy!
The Loyalty Points rewards you with reward points for every credit you buy! You'll even earn a bonus of 120 extra points if you buy over 120 credits in a given month. You can then exchange loyalty points for rares, credits and HC.