Dear laminarflow,
in theory, the use of g-flaps has a very effective role.
you says that increasing alpha, you would obtain same results...not properly.
here there is the explanation:
the use of gurney simply increase downforce coeff, improving the extent of laminar flow on upper part of the wing. This is possible, because (as you probably know, the most critical part of a downf wing is the upper side), having great alphas (AOA), you will have a separated flow more extended (in a previous part of the wing) than a lower inclined wing (more inclined is the wing, more turbolence it will create and and stall max value <). This turbolence not allow the flow to remain attached on the upper surface of wing, modifying the shape, and creating a great amount of drag.
so, the primary function of g-flaps is to accelerate flow toward the upper part of wing on the aft portion.
as you probably know, the flow goes always in the region with lower P (in our case, the lower). It's proper on the upper side that the more P coeffs create the downforce.
Here, but, the flow, in the rear part of the wing (on a configuration of std wing), has not sufficient force to overcome the great P force exisisting in that region, < the velocity (in some cases to 0!!) and creating the separated region of laminar flow with vortices (the flow, near to surface goes in inverse direction of main flow). So, with the G-flap, the flow is more forced to accelerate to equalize P differences than in a no-G-flap configuration (this, because the "bump" created with the strip of G-flap, make the flow accelerate itself over this "new obstacle"...)
I've seen real data...the drag increases, it's obvious, but total Cl is very increased!
hope this can be useful..
Lo
