I'd like to share my two cents.
One day, while answering Why were my edits rejected?, I said:
Since every site is community-driven, we try to adapt things to our reality and not the other way around. Our methods would probably not work in other sites, say Math.SX or Spanish.SX. Sometimes, when I hear the words "SE policy" said in the wild, the walking hammers from The Wall come to my mind. Don't get this wrong, but I feel it sounds like an imposition: share it fairly but don't take a slice of my pie. I prefer to look at the SE policy as an inspiration for communites to work with a predefined set of suggestions and, as time goes by, work on their own methods, adapted to their own reality.
IMHO the key here is to learn how the TeX.sx gears work as a single component. We are known to be a very friendly community, from TeXperts to newbies. Even what happens to be our policy is treated as guidelines.
Personally, I don't see anything wrong with being nice, polite or grateful to any help received. I love writing something along these lines in my own questions because I really appreciate the time and effort put in each question. And I usually "sign" my answers in this site with "hope it helps!
:)" or similar simply because I really want the OP to feel welcome, in the sense of "hi, maybe my attempt can help with your question!".
The problem here, as I see, is that we are dealing with minor edits. I'm not used to play with the review system, but sometimes we see some edits that are considered minor, like some punctuation issues or a "proper capitalization" of a sentence. Edits are surely welcome, but we can't forget that:
edits usually update the activity of a thread, that is, if you edit a 2-year-old question or answer, it will be featured in the front page and more recent threads (considering creation timestamp) will be placed in a lower rank in the list;
edits have the "moral duty" of going towards better comprehension of the thread as a whole; and
edits cannot drastically change the original text, for better or for worse.
I already removed thank you's in the past, but not as the only reason for an edit. Nowadays, I'm more in the live and let live edit philosophy. Of course, everybody has different opinions about this, but:
edits that only remove thank you notes might be considered a minor edit, hence rejected;
edits that remove thank you notes or other minor edits in old threads are strongly discouraged, and will certainly be rejected; and
edits that don't improve the text do not add value, hence rejected.
In any case, it's imperative to always leave a comment on why you edited a question or answer. We have some predefined text building blocks in Text building blocks which might help.
I'd keep thank you's. It doesn't hurt. If it's a major edit (usually code formatting), it's up to every editor to decide if a thank you note should be removed, but we cannot be picky on editing a text for the sole purpose of beating the OP with a stick just because of an act of kindness.
Internet is already a hateful place. All we need is love.