Vietnam's tourism problems are internal, not external. Foreign tourists are aware of Vietnam and its attractions, but more needs to be done domestically to make it easier for tourists to visit Vietnam, and to encourage them to come back a second time.
There are three problems that need addressing. Firstly, there is the visa issue. You recently reported that the number of Vietnamese visitors to Cambodia has increased, due largely to an easing of visa restrictions. Hopefully Tourism officials that will ease and simplify the inspection process visa to tourists can more convenient to go to Vietnam.
Secondly, you have the problem of repeat visits. Currently, 95% of visitors to Vietnam - an extraordinary number - don't come back again because there are many troubles in their travel. This gives Vietnam a very bad reputation amongst travellers, and word-of-mouth marketing is the most powerful kind. tourism employees are educated and well trained will help improve this.They will make travelers get the care and the best travel guides.This should make the whole tourism industry, not just a travel company.
Thirdly, Vietnam needs to learn what makes it attractive to foreign visitors, by listening to and taking advice from tourists and expat residents. A clue - it's not just culture, history or water puppet shows. It's cheap shopping, great beaches, good restaurants and, in Saigon at least, fun nightlife. Cultural tourists only tend to visit a place once. Holidaymakers - those who travel for fun, for cheap beer, and for lazy days on the beach - will return to a favourite spot again and again. And there are millions out there.