I have a working and reasonably-complete module that integrates LM PayPal and User Points so that users can use PayPal to buy user points (or whatever you've called them). This provides a flexible subscriptions system, with all the various userpoints modules linking in.
The site I developed it for allows users to buy PayPal "credits" and then create nodes at a cost of one credit per node. Potentially these credits might expire with time, be awarded without needing payment, and could be transferred between users.
Comments, and offers of help to maintain this (if others think it might be useful), welcome!