tedster - 4:56 am on Nov 15, 2012 (gmt 0)
I have some of the same misgivings these days about changing well-ranking pages. Some sites report no problems but others do. My sense is that if a site has a strong set of authority and trust signals, they can make changes more easily and without introducing ranking problems.
The kinds of changes you are describing do not sound very challenging. Many of them might not actually trigger a "changed content" flag at all, if the essential semantic meaning of the content is not changed but only its aesthetic nature in grammar and readability.
If you have concerns about the current level of trust Google shows toward this site, I might not start with widespread changes but rather with some low level experimental work. If you see this is well received, you can roll out more changes. But if it causes major amounts of lost traffic, I'd rethink the approach before going at it any deeper.
It does sounds like you are interested in helping your readers and that should be a good thing in the long run. If you get lots of repeat traffic rather than depending solely on new visits through search, then you may be able to weather some small shifts in Google traffic and result in a long time real gain. It certainly sounds like that is what you should expect.
I'm remembering that the Panda algorithm also can boost a page's ranking. The kind of changes you are suggesting might even help your site improve when Panda runs a data refresh.