I have this mess of wires in a junction box of a stucco house (built 30 years ago). Couple of these are going to the overhead fan in the room. Will a simple clamp meter help me identify the relevant wires?
If by "clamp meter" you mean a non-contact AC Ammeter, and if the circuit can be loaded enough to trigger the reading. Yes, you should be able to isolate the circuit using such a meter. (Keep in mind that this type of meter only registers AC current so you must have current flowing for it to read.)
On a related note, however, that box looks to be severely overloaded. You may want to consider upgrading it as this may be unsafe.