This topic is the stuff aikiweb flamewars are made of...
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.