I think it's an interesting question (or really, set of questions) that you pose . . . difficult to answer in many respects, but I'll at least try to begin, based on my own limited experience (aikido many years ago, Chinese martial arts more recently with a focus on taiji training methods). I was trying to get at the same kind of comparison and contrast in this thread:
There are lots of new, interesting questions that have surfaced for me lately.
Nice to see I'm not alone.
I'd also like to point people to a training blog being written this summer by a fellow who flew to Beijing specifically to learn and train Yiquan working directly with one of the best teachers of the art in the world today. It's definitely worth following his insights, frustrations, and experience of Beijing today: http://cattanga.typepad.com/see_otter_yiquan/
I got caught up in this blog, so I didn't have time to reply to your post. But I did want to emphasize this blog. Wow, a lot, and I mean a lot of what he's talking about has been posted here on AikiWeb.
The blog is a very good read for theory and background on internal aspects. Of course, you can't get practical out of it as that requires hands on training. But, quite a bit of commonalities in there.
I'm still reading ...