Edit rejections are something that comes up in meta on every site I've used, including MSE... Every site has their own idea about what makes something fall under "no improvement whatsoever". I tend to focus on readability while letting the OP maintain their voice... and that's even when I have the ability to edit without approval.
Do we want questions to be clear and readable? Most definitely. Every site has a six-character minimum for edits when you don't have sufficient reputation but even single-character edits can be vital to a post's readability. The six-character limit is designed to encourage newer editors to find more than one error to fix, as it's not uncommon for a post with one error to have several. We should be reviewing the entire post when we edit, not just one small part of it.
I personally see the edits you made in your example to fall more into voicing than readability but it really depends on the site. "Gonna" is normal vernacular, particularly on the informal world that is Arqade (I assume a Skyrim question comes from Arqade). Starting a sentence with "but" may be a bit messy but it's not really that big of a deal.
The "no improvement whatsoever" text reads:
This edit does not make the post even a little bit easier to read, easier to find, more accurate or more accessible. Changes are either completely superfluous or actively harm readability.
We should take this explanation quite seriously and welcome any and all edits that actually improve the question, regardless of whether we consider them "trivial" but that doesn't mean that we need to edit posts to remove any personality from them.
So, yes, please change unnecessary abbreviations, grammatical errors, spelling issues, punctuation and formatting but be considerate of the OP's voice when doing so. As long as you can make your edits pass the 6-character minimum, please help improve the posts here and, if you're reviewing, please take the time to look at the edit and see if it fixes valuable things. I've seen several edits rejected (on other sites) that I think should have approved but because all they did was fix a letter or two, they declined them as trivial... that's not the definition of "trivial" when it comes to edits, though. In fact, the word "trivial" doesn't appear anywhere on the rejection reason list.
Remember, there's now a feature that allows the OP to unilaterally reject (or accept) an edit even after it's gone through the review queue. So, if the OP actually liked your edit after it's been rejected, they can accept it and you still get the points... but if it's accept it and they later reject it, you lose them.
I don't really see that there's a difference between how we should react to this between public and private beta.