I hold the opinion that the most important practice is the power off to the ground. Applying the power at 300 feet, and saying that you could have made it is really cheating yourself out of the most important part of the practice.
When I'm training, I would much rather the pilot pick a close field, and get it down, than to bob around searching for optimum glide characteristics. Yes, if you're off shore, or over the city, making the glide stretch to the next suitable landing area is important. But, a lot of our flying affords us reasonable choices nearer - make the most out of those.
This is when you add 10 knots for the wife and kids, and maintain your inertia down final, you'll be happy to have it when you begin to flare. This is what the overshoots miss - transition from glide to actual flare and land. If you arrive to the top of the flare power off with landing flap, and at the "best" glide speed, you're going to have to time your flare really well. It's fine if you're practiced at it, but if you're not, that extra inertia will come in really handy. You can slip it off, if you have too much as you cross the fence - but you're going to loose it in a hurry anyway.
If your flight manual suggests an after takeoff speed, this is the speed you're looking for for the final segment of the glide to a power off landing. It's probably around Vy. This faster speed provides the inertia you need to flare and land. It's easier to find the close field, and not be distracted, for a good landing from the faster approach speed...