While I've only ever made it up to Gold with Avianca Plus, i have the latest (January 2008) paper membership guide, which clearly states the following as benefits for Executive Platinum with regards to upgrades:

- unlimited free upgrades to business class on Colombian domestic flights upon check-in at the airport if space is available
- 6 upgrade certificates to Business class upon qualifying for Executive Platinum
- 2 additional upgrade certificates every 10.000 miles flown with Avianca as an Executive Platinum member

So the agent in MIA was correct.

You need 1 certificate to upgrade each one-way international flight in zone 1 (Panama, Ecuador, Venezuela, Caribbean, Costa Rica), and 2 certificates per one-way international flight between Colombia and the rest of the world (independent of fare class paid).

Please note that upgrades with certificates can theoretically be confirmed anytime after booking. Since they book into award class A, however, I have noted that it's difficult to get these upgrades confirmed on routes with a lot of business demand (e.g., BOG-CCS). I don't know if it would be easier for an Executive Platinum to confirm these upgrades.

In general, I'd say that being Avianca elite is about the same as being elite with a US carrier. The lounges are nothing special, but at least you get access. And the same applies to business class on domestic flights.