If it's good grammar and You respond to following questions then it's good.
I think comments should reflect the post. Are you really gonna comment "A nice article" when some wrote long one, mostly not. I bet you can come up with questions or ideas you'd like to share :P Short comments are however suitable for art in my opinion, because there really isn't much else to say sometimes, but "Really nice, well done!".
And this leads to another topic - how to comment. Short comments feel lazy and aren't engaging. But they aren't spam in my book.
Spam comments are more like "hey, nice shot" while the post is not about the cover picture at all.
Is it acceptable to acknowledge that you upvoted and resteemed a post?
sure, but the problem is some are abusing this by simply copy-pasting the same line everywhere while not even upvoting the posts. That's why it's always better to link your comment with the contents of the post in some way, to show you are not simply fishing for votes, but sincere.
It can simply be something like: "I liked this and that about your post. I upvoted/resteemed...".