Rob,
Winglets reduce the induced drag generated when operating at high lift coefficients i.e. high angles of attack. This provides benefits during take off and at high altitude cruise. When flying near the service ceiling, indicated airspeed will be low and the lift coefficient high. In these conditions, winglets are effective in reducing total drag. Most 360s, however, spend most of their time flying well below their service ceiling at relatively low lift coefficients. At these lower altitudes, the extra parasitic drag caused by having the winglets outweighs any reduction in induced drag they provide. It is the mission profile of the plane that will determine it they are worth investigating.
Chris Zavatson
N91CZ
360std