I have an argument to this.
I always post "I have upvoted and resteemed. I also started following you so I can see more of your work." I don't post that on every article I read, just the ones that I agree with , that I feel are beneficial to the website. I make the assumption that people like to be told when they have good work, and when someone out here feels they are contributing. I don't mean it to be spammy, nor have I ever put thought into people flagging me for saying that they are doing more than just posting a picture of a kitten, and putting "Happy Monday" underneath it.
When do you draw the line between people trying to give you a compliment, and people trying to spam?
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...".