Maybe the best place to look for resources on the issue is at the Rum Soaked Fist forums, which have plenty of seminar announcements and angry discussions about all things related to Chinese martial arts. I have hooked up with people on there in the past, and it got my foot in the door with CMA.
The only universal thing I've found in my own training with respect to all this is that the internal label is a red herring. If there is a physical attribute that can be isolated and trained in the depth, that benefits movement in general and not just some technique, to the measurable benefit of one's combat abilities, then it is worth training. Such attributes do not seem to be gained by osmosis efficiently through just practicing technique or sparring, and likewise do not seem to directly translate back into combat ability without effort to make them.
My own training, though, has been focused almost exclusively on explosive power, for which the benefits seem more obvious, like move quicker, react faster, hit harder, but improvement has been damned slow most times and carry-over to anything aikido-like has been nonexistent. I still think it is cool stuff, though.
Good stuff! I too see similar things in my training, as I have friends who are in CMA and I have dabbled myself in it with them. Per my reading of some of the Tai chi texts and that of concurring with Tai chi authors such as Waysun Liao, and others, for example. Point to Internal power as something that isn't seen, not noticeable, not readily detectable, and stuff. This is indicated by the Chinese Character written for Chi. Which is represents a pot with a fire beneath giving off steam. Chi then being, air/steam, according to those in CMA, is applied to the idea of breathing.
Internal power may simply be the act of breathing that results in forces. Possibly paralleling the forces that result from exhaling. We can move things with our exhaled breath. For instance, when we exhale strongly we can blow out candles, a force results. In corporate this crude example, oxygen is fuel for the fire. Or, the steam engine model.
I feel idea of internal power is layered with complex ancient mythology, specialized language, abstract cultural elements and concepts, to say the least, all resulting in an unique construct. A construct very elementary in its inception as indicated by the Chinese character for Chi which is the source, the fuel, for internal power.
As a result, no particular concrete attributes are identified. It seems to me allot goes into discussing the concepts and subjective parts of the internal power construct, and very little into anything else. For example, it is like discussing the conceptual elements behind the forces of the steam from a boiling pot of water, but very little if any on the pot, the fire, or fuel used, all relation to the graphic symbol to represent Chi of the Chinese language. How the steam is discussed is very abstract. This may be due to the limited understanding of the Chinese observing the forces of steam and the how and why of these forces at work. That is in comparison to what we understand today about such things.
This abstract concept of internal power as a result of various readings and discussions has lead me to believe internal power doesn't have a concrete identifiable definition in its application, resulting in the opportunity for a variety of explanations and open interpretations. That is we can hang any favorable result on internal power that isn't readily identifiable. For example, very much how we use the word magic and attribute things to magic. Like, explaining how cell phones send and receive transmissions, to my nephew, without a Ph.D. I say it is magic.
Internal power, as I have concluded, is an elaborate explanation for a simply physical result, like blowing out a candle or the steam from a boiling pot of water burning the skin or moving the lid, that isn't readily noticeable, or hidden. This leads me to believe the really is no road, rather a general, unspecific label, such as the word container, applied to techniques. That internal power, isn't a competent of technique or a technique itself, rather it being a concept of power or force with a desired result, that has a label, like home run.