The graph above compares the annual total number of air & sea trips to Scilly (divided by 2 to make return trips) and the cost of a one way ticket by air (from Lands End) or by ferry (from Penzance). Whilst cost of travel is not the only issue that might affect the attractiveness of Scilly as a tourist destination it is the one most often quoted issues along with the uncertainty and inconvenience of travel.
The cost of traveling by air has risen by between 19% and 33% above the rate of inflation since 2002 (rises vary by route and which inflation index you use). The cost of travel by sea has stayed broadly the same since 2002 or dropped (if using the RPI index).
The fall in passengers is due to the long term downward trend in air passengers with a steep drop since 2012 (before BIH ceased in Nov 2012)). Ferry passengers number have been broadly stable by comparison and have risen significantly following the closure of the BIH service (ferry was extensively refurbished prior to 2013 season).
The loss of visitors has obviously had a painful economic impact. The tourist spend in 2011 was estimated by Visit Cornwall (Value of Tourism Report) at £34.3 million. There is no published report report for 2012 (perhaps a victim of budget cuts) but it seems impossible that the Island economy has not lost in the region of £5 million a year given the reduction in visitors over the last 2 years.
Data can be found here .
Data does not differentiate between day visitors and staying visitors/residents.