Back in July of 2007 I posted a comment about these two terms and how they are misused, by just about everybody.
Agendas: Everybody has an agenda. Would a voter really want to cast a ballot for someone who didn't have an agenda? Don't voters want to know what candidates for office have in mind? Why is having an agenda a negative? Let's use the concealed carry law that went into effect here in Kansas. By letting folks know where they stood on this subject then the voters could vote for/support those candidates whose agendas were in line with the particular voter.
Special Interests: Same thing here. Using the concealed carry issue, those organizations that supported the idea also supported politicians that thought the same. And, the reverse is true. Organizations that were against the idea supported politicians that thought like they did. Both types of politicians were supported by special interests.
Rather than use these terms as negatives, use them for information.