Both subjects are different. Therefore, it's not possible to deem your success based in possible links between both. The theory I've heard is that practice doing Specialist maths questions benefits your understanding and grasp of concepts in Maths Methods, meaning increased competence overall.
I took tutoring for GMA this year while doing Maths Methods at home. Honestly, the only difference I found was that I was more motivated to GMA work outside of school and focused on it more throughout the year. I also acknowledged its difficulty right from the start, and made it part of what I did everyday, in addition to homework, school tasks, etc.
If you haven't already, take a textbook and familiarise yourself with the concepts of both subjects. Ask yourself, what you feel needs more practice and greater requirement to understand. It's really your ability that judges whether you need tuition or not.