Ministers hoped interest in genealogy among the 50 million Scots descendents globally would underpin events next year. Estimates suggested the economy would reap up to £500 million from visitors trying to trace their ancestry.
But new VisitScotland research questions whether the present income of £100m a year on the global genealogy sector can be increased five-fold by 2014. The audit by Dr Bruce Durie, of the Ancestral Tourism Steering Group for Scotland, followed up on the tourism agency's original report.
He pointed to difficulties with the estimates, such as concerns that events such as the Commonwealth Games fall outside June and September, when interest in such tourism is at its height.
Mr Durie added: "VisitScotland staff on the ground have limited information on which to give visitors the appropriate advice on ancestral tourism."
The findings follow concerns the Year of Homecoming will not attract the number of visitors hoped for.
Murdo Fraser, convener of Holyrood's Economy and Tourism Committee, last week criticised Homecoming plans in the wake of the fiasco of the 2009 Gathering in Edinburgh. A 2014 Gathering was axed amid projected losses of £250,000.
Mr Fraser said: "There are real concerns we are missing out on a market with huge potential."
Patricia Ferguson, Scottish Labour's culture spokeswoman, said: "There are real concerns the latest Homecoming event is based on the same kind of inflated assumptions that caused the last event to result in disaster."
A VisitScotland spokesperson said: "The findings were enlightening and have led to a focus for activity in this area across the organisation. In the next few weeks we will launch our Ancestral Tourism Guide with Tourism Intelligence Scotland, which will provide advice to the industry on the best ways to build on this audience.
"We continue to work closely with key partners to ensure the 2014 programme has a wide variety of events designed to appeal to these audiences."
A Scottish Government spokesman said: "Planning of Homecoming Scotland 2014 is progressing well.
"The programme already includes a significant number of events and activities celebrating Scotland's rich ancestry."