The political parties are largely a holdover for the past, a place for people with similar real life and NationStates political views to come together and discuss policy. They were more active before but are now pretty quiet, they were just never formally disbanded and no new civic organizations were created to knock them out of their place.
Ultimately though, they are private civic organizations whose existence is guaranteed by the right of association, so we can't legally ban political parties as a whole. More importantly, the important question, I believe, is not whether political parties are useful for us as a region but the general management and purpose of the board. I do think having a place for civic life and organizations is important but the old policies about what groups warranted sub-forums and processes for dropping sub-forums and special groups have fallen by the wayside with no one to create and maintain them.
Broadly speaking, if we keep the Zocalo I see two possibilities, one where its the responsibility of forum moderators or admins and one where it's the responsibility of some political office.