Incident response teams share information about threats, exploits, incident response tools and techniques through contact at the conference, and through the technical colloquia and mailing list. It also gives other teams a chance to meet the newer members of your team. There are other security conferences. Some provide limited training in incident response, but none of them address the specific needs of incident response teams. This has helped at least one team tremendously in its outreach efforts to local businesses.
Internet security is an international problem, and needs an international involvement to address it.
You may need to contact another IRT outside your country to address an incident at your site. Knowing who you are working with before you contact them in an emergency is a great help, and can result in more effective and efficient coordination and interaction. It is important to raise the profile of your team in the international incident response community to establish these contacts. It is especially useful for meeting teams from the area where the conference is located, which you might never meet otherwise. International travel isn't necessarily more expensive than other travel.