I'm having similar problems. My use cases are:
- Get only the users whose profile data has changed since the last time I fetched them (the 'user' table has the 'timemodified' column, but the web services do not allow me to use it for filtering the results)
- Get the timezone of each user (available only in some of the functions)
I already made initial patches to the latter: https://tracker.moodle.org/browse/MDL-60240
Hopefully shortcomings like this get fixed to the existing web service functions. It doesn't make sense that site owners need to reinvent the wheel for such minor differences in the requirements.