For an S10 user, I don't see a real great reason to upgrade except to have the latest and that's just a preference to throw money on a hobby/interest IMO.
Because it really comes down to asking yourself... Is there something on the S20 that's so much better on my current or not on my current phone that I need now to play?? That's just gonna make my current phone look old??
You gonna be left behind in proccesor speed?? No
Gonna miss out in being able to download at 1000 megabits with 5G around town?? No.
Can't live without 120hz? Really can't go back after seeing it?? No.
Camera is going to be night and day better than the S10+ or need that 100x zoom?? Jury out.
The battery increase will give me an extra half day of use?? Dunno.
Do all those changes make the S10+ fall so far back that it makes it worth the cost of the new??
So, personally, put it all together I don't see the need and I wouldn't if I had a S10+.
I have an Note 8... so I am thinking about it. I probably could still enjoy it for a 3rd year really. But even then I'm not running to pre-order and buy one tomorrow... and that's with me getting corp price at $899.99 for an Ultra. I can probably wait and see what they do for the Note 20. I may change my mind after checking out the demo at Best Buy this weekend.
You S10 guys are going to get Android R and OneUI2.0 so software wise you should be same as S20...