[aerohead]

It seems that the VG is intended for the notchback in which separated flow fails to reattach onto the boot,yielding a squareback wake.
The Mitsubishi Lancer suffered from this as well as a Honda Accord.
Successful VGs were sized and spaced with critical dimensions specific to these vehicles.
The Beetle has no rear structure for which to enable reattachment.
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In free flight,there exists an axi-symmetrical flow field which provides a jet pumping action behind bluff bodies,which attempts to pump air into the turbulent wake.
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In ground proximity there exists no axi-symmetric flow field,and no jet pumping action.
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While VGs might reduce the effective wake of a cargo plane,they have been shown during wind tunnel investigations to offer no gain within ground proximity,as well as many other aeronautical technologies.
Hucho says they're a dead end for ground vehicles.(unless there's a structure behind the separation point)
------------------------------------------------------------------------- Ernie Roger's Beetle wing provides a structure in which the longitudinal vortice pair can be burst,and a locked-vortex can be captured,allowing the outer flow a 'surface' to ricochet off.