I have also been a long time S4 SS user. Few months ago, I compared my S4 SS to S9 SS and recently did the same but compared it to S10 Titanium. I didn't like that now Apple forces one to pay for Hermes edition to have Silver look vs the standard S10 Titanium models which have different shade/colors.
At the end, I found a great deal on S8 SS (new in a box) and also sold my S4 SS. Factoring that it would cost me $100+ to get a new battery service in my S4 in coming months, I essentially upgraded to S8 for about $100 - could not be happier with the outcome.
In my opinion, S9 / S10 feels like a total disappointment and waste of money if one needs to spend $800 when going from S4 SS.