We have a credit system as well. If you consider this, you need to consider the potential value of the credit system or point system. You want it active enough so that people 'feel' it and know it's working. However, you don't want to give away your store.
As more indie's consider a $2.00 or $1.00 price point it's hard to maintain a credit or point system. This has been a stumbling block for me as I consider a new price structure. Do I drop it all together or modify it (the credit system)? Because people like it so much, I plan on modifying my system.
Simply more to consider as you dabble with price and day changes.

Chuck