You may wish to keep in mind that in the event of a serious accident, it may take months before liability has been resolved. A Mexican citizen may request that the "other driver" be kept "in custody" while the insurance companies or company wrangle things out. You may have insurance, even increased limits of PL & PD but until things are resolved, the foreigner will sit in a prison (I did not mean jail). This may take months.
The "legal aid" option as found with most surplus line broker insurance companies allows them to cut an immediate check to the court that guarantees that a debt will be paid regardless of the willingness or unwillingness of "the other party" to accept payment in the long run. In the real world, this allows the foreigner to be released from custody usually within 48 hours.
To verify this point do so by contacting your surplus line broker.
And yes, the long and the short of it means that you can carry the best Mexican insurance but without an optional rider you can end up in prison for months in the event of a serious accident.
I hope this helps you.