I just purchased a refurb iMac Pro, if I wasn't told it was a refurb, I wouldn't know.
I've just been reading your posts and from what you're saying, I doubt you need the latest and greatest. If a 2010 has been "working" for you up until now, a 2017 will likely last you until 2026.
Pick the option that seems most affordable to you.
Actually, I haven't been using an iMac for several years. I have been pretty much all in with my iPP. I'm just realizing now there are things I could do if I went back to a desktop that I can't do on my iPad, or at least not without a lot of extra effort.
However, to decide if I would really use one, I hooked up my dd's and have been using it for the last few days. I'm finding it's not terrible, so yeah, I think I could easily do okay with a refurb.