"Other than cricket I can't think of many other ties other than pretty tenuous links with a small island," Mr Shearer said.
He acknowledged Barbados would have strategic value for winning votes from Caribbean nations for New Zealand's United Nations Security Council bid, which he said was an important goal.
Mr McCully stressed it was not a trade-focused posting but a tactical one.
"One of the challenges is that bigger countries, particularly at the United Nations, are looking to occupy more of the space, particularly in time on the Security Council, and that can only be at the expense of smaller countries. Unless smaller countries that have the same sort of strategic interests work together we're not going to improve our overall influence and that should be a long-term project for us."
He said placing an ambassador in Bridgetown made perfect sense because Caribbean nations faced similar pressures to Pacific Island countries, in particular oceans and fisheries management, climate change, and renewable energy.
New Zealand played a leadership role in the 16-member Pacific Islands Forum, and could now apply its international policymaking to the island states 10,000km away.
"New Zealand's international personality is strongly influenced by its Pasifika roots.
"And I think that alliance with the Caribbean nations is very important and very natural," the Foreign Minister said.
Mr McCully said the next "obvious" continent for expansion was Africa, where New Zealand now has posts in Cairo, Pretoria, and, as of this year, Addis Ababa in Ethiopia - home of the African Union.
"There are more diplomats in Addis Ababa than there are in Brussels," Mr McCully said, noting that the post provided access to 54 countries.
New Zealand was also considering posts in Nigeria, where Fonterra was aiming to capitalise on a market of 200 million people, and in Bogota, Colombia.
As part of a Ministry of Foreign Affairs shakeup last year, the embassy in Sweden was closed.
Other posts in Madrid and the Hague could also be closed.
