As RP's we returned to Mexico last June pulling a cargo trailer with our possessions in it. We had been residents too long to use the menaje de casa. No customs broker was interested in us because we didn't have enough stuff but the value was well over $3,000.
Contacted our local Mexican Consulate in Oxnard, California and they said that what we should do legally was to arrive at the border and declare everything and pay the tax. We did that. Total cost $3000p, 45 minutes.
According to the Consulate it is perfectly OK to arrive at the border, declare what you have and pay. Credit card payment required, and official paperwork was given to us.