Hi,
CustomerSyncService is not meant to be used as a change history tracker; it is more meant to let you know what objects to sync when syncing between your local server and the AdWords server. If you get TOO_MANY_CHANGES error, you should either reduce the time period to see if you can get a valid response. If this doesn't work, then you should resync the whole object.
Cheers,
Anash P. Oommen,
AdWords API Advisor.