Either case (Settling with insufficient power or vortex ring state) are unlikely to sneak up and bite you, as both take a reasonable amount of cue-ignoring by the pilot.
For "insufficient power" the training technique that helps might be something I have taught for a while - the controlled power approach. Simply said, it is a progressive slow down and power check as you make the approach so that you never find yourself committed to a hover while overloaded. Most instructors teach something like this, perhaps not formally, but certainly trying to spark the judgement. These techniques are obvious to experienced pilots who have flown overloaded helos for a living. I operated an AH-1G in Vietnam that could never hover above 1 foot at max power, any technique but the one below spelled doom:
1) know the power you can pull, the max power, before you start the approach. Easy way, at 500 feet above the landing, just increase collective, climb, and note the max power (where you reach the first limit, of course). Since you are somewhat higher than the landing point, the check will be slightly conservative. Note that power, and don't forget it.
2) As you enter the approach, spot the max power on the gage. As you slow the aircraft down and keep on the approach line, watch the torque begin to increase. Slow down gradually and note the power increase as you pull up on collective to keep the approach angle constant.
3) As you get quite slow, perhaps in the 25 knot range, the power will start approaching the max power that you observed. Slow down carefully, feeling yourself increasing power as you slow. One knot is an appreciable change. If the power gets within 5% torque of the max, be very careful not to slow any further unless you are SURE things are healthy. Most insufficient power accidents are made right there, when the pilot slows abruptly and inadvertantly commits to the hover, without having enough hover power.
4) If you reach the max without assurance of being able to arrest things in the hover, go around. Simply keep the power where it is, gently lower the nose a hair, and you will start to accelerate. Increase power to the max and you will gently climb. It is impossible to "fall through" on approach if you keep the power and speed under your direct control.
5) recall that a bit of ground effect will help you at the bottom, so if you have almost max power and a very gentle descent rate, all will calm itself as you wash into the hover. Note that the peak power you pull should be at about 10 feet or so, and it should be almost exactly the hover power (maybe 1% more at the most) if you have done things right. I have made this a game with students, to see if they could sneak the aircraft into a hover with only hover power as the max pulled. It is great sport, and teaches the soft technique that will keep you able to fly at the edge of your aircraft's performance.
6) Note something interesting as you practice the sneaking into a hover - the control that causes you to pull too much power at the bottom is almost never the collective, it is the cyclic, because you are decelerating too rapidly, and the "whoa, Nelly!" flare at the bottom will always cost you more power than a steady hover.
7) As solid confirmation that you have the controlled power approach down pat, try making a go around during the approach with your hand off the collective. Here's how - at some point, just remove your hand from the collective, and then gently lower the nose maybe 1 degree. As you accelerate, the extra speed will get you closer to best rate of climb speed, so you will start to gently climb. If you are rushing the approach, you will sink quite a bit before you climb, a sign that the approach is a bit too fast for a maximum performance technique.
8) You are ready for graduate school in this technique if, on a calm morning you can actually plan a touchdown at a spot with your hand off the collective while decelerating through the 30 knot point. Gentle speed changes will change your approach angle, and the smooth cyclic control will help you a bunch.
Here is some discussion on VRS:
http:
www.s-92heliport.com/vrs.htm