I personally think a good practice might be to edit the answer yourself, and remove the unimportant stuff. If others agree, they'll approve the edit. If it's really not important to the answer, I would think the questioner wouldn't be terribly offended. I've had similar stuff happen to things I've written before.
IMO, downvotes are a lot harder to deal with in the long-run than undesired edits, even if you don't agree with the edits. At least you can see that the editor is trying to help, and is putting in some effort to do so (even though it might not be obvious for a short time, while you're fuming about the perceived vandalism). Some people will be grateful (rather than upset), however. Plus, anyone can look at the edit history to see your original answer, anyway (they can see that someone edited your answer, and who it was). I personally like to look at those. Plus, the answerer can always roll it back, if it was really important (and will possibly feel obligated to say why it was important to leave it how it was).
Edits are nice, because they show the answerer how to improve instead of telling them. Some people learn better that way.
I don't think you need to worry about making enemies here. Making your POV known is a good idea, and people can understand what you mean. It's possible you might hurt some feelings, but I'm pretty sure you'll be forgiven and appreciated with what I know about this site, so far.
It also might be helpful to instruct them on a few key points:
- Comments aren't meant to be permanent, while questions and answers are (if people are posting long comments as answers, that poses some problems, because they're harder to clean up when they're no longer needed). If they understand that comments aren't meant to be permanent, they may be less likely to give really long ones.
- You should never post comments as answers, especially if you know better (at least that's the impression I get). If you want to write a super long comment, you can always write it on pastebin and link to it in a comment. Because comments aren't meant to be permanent, it's not the end of the world that you're linking off-site for it. If pastebin disappears, the world will still go on, because it was, after all, only a comment. However, I think a lot of the comments on this site in particular are very useful while they don't necessarily fit into the question/answer (as in, I don't see a need to clean some of them up, even after all the questions/answers are edited). It's kind of a difficult situation for a gardening and landscaping site. I don't think that many people realize that comments are meant to be temporary, however (so some might question the use of pastebin for a long comment on grounds that the link might break some day).
If you weren't as used to StackExchange as it seems, I might tell you more stuff, like high rep users and professionals often need to know a lot of details about the question (including ones like this), and they may answer differently if they perceive that your need is not what you're asking.
People don't always get things from context on the first read. So, it helps if you more than hint or allude to what you want in your answers. If it doesn't say it in explicit terms, you can expect to be misunderstood. In fact, it's not a bad idea to expect it even if you do (but it's not your fault then). I mean, you might want scientific figures where people think you just want a basic idea. You should tell them you want scientific figures if that's what you want (although I'm pretty sure most questions that would ask for such are off-topic, and better suited to other StackExchange sites). This site generally deals in practical problems that need solutions, rather than merely questions that desire answers (it took me a good while to accept that). You use at least one other site like that, I see (so, you probably know what I mean all too well).
So, I'm saying, one way to help improve the answers (whether a high or low rep user is answering) is to improve your question. Not to say it was a bad question, but it can always be better. If the user is high-rep and active, odds are higher than usual that the same user will edit the question to something more appropriate after you edit your question to answer those misplaced questions. If they don't remove the questions from the answer after you answer them in your question, I think it's perfectly fine for anyone else to remove them (but it is the answerer's responsibility, I believe).