I'm happy with the functionality of the basic tier and there is nothing in the Pro tier that I feel I need. I would like to support development however I don't want to spend the full price of the Pro tier when I don't need any of the Pro tier functionality.

Can I suggest you add Supporter tier for those who are happy with the functionality of the basic tier but wish to make financial contribution to support development. I would suggest either a fixed price of $20/year or ability for user to set their own donation amount.