They contribute to very specific aircraft aerodynamic effects but everything else depends on ... location, location, location. Without CFD/tunnel testing on your particular vehicle shape/forms, applied at wrong locations these things may not contribute and even cost aero-efficiencies.
NASA - Micro-Vortex Generators Enhance Aircraft Performance
http://ntrs.nasa.gov/archive/nasa/ca...2010003963.pdf
http://www.mitsubishi-motors.com/cor...004/16E_03.pdf