Mr Richardson said the elevated NZ currency made New Zealand more expensive as a destination, potentially discouraging some visitors.
"In addition, visitors may be working to a fixed budget in their home currency while travelling. An appreciation of the New Zealand dollar erodes the value of that fixed budget and will lower the total amount of spending in New Zealand dollar terms.''
Mr Richardson noted the NZ dollar was relatively low against its Australian counterpart "a factor that may encourage a higher proportion of Australian visitors as well as a higher average spend''.
"However, New Zealand must still compete as a destination for Australian tourists during the Rugby World Cup.''
Mr Richardson concluded the $700 million spending by overseas visitors was equivalent in magnitude to 1.4 per cent of New Zealand's GDP but that spending would not be a direct boost to GDP.
Significant domestic spending during the tournament was also expected but it was unclear how much of a total boost that would provide.
The net impact of the tournament on both short and longer term economic measures "remains to be seen'', Mr Richardson said.