I have been flying with the original props for almost a year now with no visible cracks. Is it a good idea after a long period of time to just replace them with new ones even though they look ok?

Generally, there is no need to change the propellers if there is no damage. In considering that you have used it for one year, I would suggest you to replace.

You can always check the online store under your product's accessories for props or any other accessories that we would have available.