From my 9 to my 10 there isn't a ton of difference. I love the 45w charging and I perceive the camera to be better. I dislike the left side power button more than I could possibly say. I'm a wallet style case user and I've yet to find the location of the power button easily without flipping the case open.
I don't know much about the S9 or the S10. I have the Galaxy A50 and it's a great phone for me. Personally my opinion to your question I would say don't upgrade right now. I'm going to jump on a limb and assume that you couldn't have had your current phone for long since this whole line is new. You should keep your current phone (S9) and just enjoy it. Just because the S10 is on the shelf doesn't mean you need to quickly get it, because I can almost guarantee you that there isn't much of a difference between the two. I think you should just enjoy your phone now. There is nothing wrong with it. I can probably guess it works perfect and really the only thing you would be accomplishing by upgrading right now would just be wasting valuable money that could be used for something far more important. Don't upgrade unless you really have too. Maybe if your phone breaks and it beyond repair, or someone steals it. If you're going to upgrade make sure there is a strong reason behind why you're deciding to purchase the S10.
From the 9? Not unless you have a free upgrade honestly.
Love my 10+ but I would still be using my 9 if I didn't have the free upgrade. I don't like the moved power button and I miss the fingerprint scanner being in the best possible location imo. Otherwise not a big enough upgrade to spend the money on.
I didn't upgrade from my Note 4 until the 9 because I had Oreo on my 4 that ran great and nothing between the two caught my eye enough (I did have the Nexus 6P in there but went back to using my 4 when I moved and had to change service). Phones aren't advancing anymore like they once were, better to wait a year or two between upgrades if you can when not on an upgrade program. Even then, if they butcher the 11 I'll skip it.
I upgraded to the Note 10 Plus 5G and absolutely LOVE it!! The camera is phenomenal and the photos that I've taken are absolutely amazing. There is so much in the Note 10 plus that I have had it for 2 months now and am still learning new things every day. And that's fun!