Seeking a point/level module to encourage user activity
For various voting and similar systems you could check these modules (including some quotes from their project pages):


Voting API:



  ... helps developers who want to use a standardized API and schema for storing, retrieving, and tabulating votes for Drupal content.



Fivestar:



  ... adds a clean, attractive voting widget to nodes and comments and any entity.



User Points:



  ... provides an API for users to gain or lose points for performing certain actions on your site. In conjunction with other modules, such as the Userpoints Nodes and Comments users can accumulate points for actions such as posting nodes, commenting or moderation duties. 



Flag:



  ... is a flexible flagging system that is completely customizable by the administrator. Using this module, the site administrator can provide any number of flags for nodes, comments, users, and any other type of entity. Some possibilities include bookmarks, marking important, friends, or flag as offensive. With extensive views integration, you can create custom lists of popular content or keep tabs on important content.