Well domestic tourism refers to the principle that the inhabitants of the country place a considerable (or lack of…) amount of money in the tourist trades. (Primarily the service sector)

International tourism would focus on the principle that whatever the interest, the tourist is attracted to the [service sector] location because their interest and the money derived from their visit is obtained and accounted as revenue for the service.

Use the money value of each to compare… or that’s what I would use. Use the service sector as the comparison point.

I would point out the fact that international tourism deals with much older and established forms of interest (arts, architecture, mountain’s… etc. thus drawing people that do not have access to the goods or resources in their home land; or even the fact that there may be a more diverse amount at the new location) versus domestic tourism usually having a more “laid back” focus. (people usually exploit their interests to their full potential in their home country; with the understanding that they have the ability to travel and such)

The importance depends primarily on the type of economic system that the government of the country has chosen. In a capitalistic form, the service industry is enormous; the revenue accounts of a massive amount of the GDP. Thus with the removal of the the service, GDP would decrease. The amount of decrease is in respect to the discontinued service.

Now in a communist form, “everyone is equal”, so the service sector holds little sway in comparison. You could simply issue a new allocation of services or goods.

I would measure the effect of GDP / GNP to determine the overall importance of each.