How is the OP calculating the amount of compensation that would be reasonable? The standard shouldn't be to pay enough for you to vacation later in CUN but rather to refund reasonable costs of your "trip in vain." What did you pay for nonrefundable hotel charges, including the airport transfers? That amount, plus phone fees and the cost (including photos) of a new passport, would IMO be reasonable in addition to a refund of tickets for OP and spouse. Since there were personal activities undertaken (successfully) in SLC, the OP should pay for the hotel there and costs of getting to/from airports in SLC and at home, including airport parking expenses.

There may have been some career advantages of participating in events at CUN but these lost opportunites can't/won't be compensated.

ADDED. I would expect DL to also give you some redeemable miles for your inconvenience.