I have found you should service the drive pins and diffs regularly, check bearing if there getting rough and only replace other parts if there worn out or broken.
One track i race at I have to do this after every meet and other tracks i run at every 2-3 meets, bacically the type of surface determines my service intervals, some are very abrasive and some not so bad.
Getting a new buggy, the question you ask your self will it make you faster, proberly not.