I am trying to two do things...

(1) Display points as currency — instead of 2000 points, I'd like the points to show as $20.00 (most notably on /user, but really across the entire site).

(2) Allow points to be redeemed as currency — instead of entering 1250, the user could enter $12.50.

The points can still be stored as an integer, so I don't think the decimal issue applies.

@bobojo has helped me on the admin side using function MYMODULE_form_userpoints_admin_txn_alter, commerce_currency_amount_to_decimal and commerce_currency_decimal_to_amount. This allows admins to add and remove points as currency (i.e. on admin/config/people/userpoints/add).

However, I can't seem to find the function to do this same thing on the checkout discount pane.

As an aside, it seems as though other people are looking for the same thing: