In order to manage the teams, matches etc. the logged in user must have the Worldpress capability
wcp2010_manager. By default
the plugin adds this capability to the Administrator and Editor roles. If the World Cup menu option is not available verify that
the currrent user has the
wcp2010_manager role. You may need to install a capability manager plugin to manage roles and capabilities.
Yes, you're right, logged in users only. Allowing entries for visitors makes it difficult to validate a visitor when returning to edit a prediction or view previous predictions. You effectively have to use the combination of name and email address etc to authenticate a user. WordPress already has all these features so why re-invent the wheel.
A previous plugin I wrote for predicting Formula One race results had the option to allow prediction for visitors, but I found that the vast majority of installations did not use this feature.
The few that did, caused headaches for the system Admin as people forgot their names/email addresses, and the admin had to manually correct/merge entries. It was also possible for someone determined to hijack someone elses entry. The was some security to prevent this, but certainly not as robust as the WP login system.