Cub:

Fuzz uses the same analogy I use: if your best L/D = the headwind, you aren't going anywhere...and generally, you want best glide to actually make some useful distance (such as not ditching when you have 4 gallons of fuel remaining...)

The important point: while L/D max is a certain Angle of Attack, and while one must generally increase the speed into a headwind, it will never be as good as could have been at no-wind L/D max.

But it is better than having a groundspeed of zero.

This works for optimum cruise speed in low-drag airplanes, as well (although I have not found this to be true in airliners). In the T-38, I came up with an empirical formula nearly a decade ago to increase cruise speed in a headwind; slow down with a tailwind. We got a "divert profile" software mode a few years back, and it validates my formula within about 3-5 knots.

There is a point of diminishing returns, of course. In the T-38, that limit is about 350 kts: the drag rise starts to negate any gains above this speed.

In a light airplane, power-off, trying to glide 150 kts probably wouldn't work either. Point is, the change in airspeed is a function and fraction of the wind affecting your progress.