Its not overkill, removing the thermostat and flushing in the reverse flow removes shit that has become stuck in the normal direction of flow.
If your technique is used, the system will not be completely flushed and if any other type of coolant is used besides the type that was originally in there, it will be useless.
If your in a hurry and are using the same type/brand of coolant that is already in the system, use mitch13's method.
If you have got time and want to do the flush correctly, use the method I said earlier.
Do not mix coolants.