Overall, it depends on the system if it saves time/effort or not. If the changes are infrequent and basic, you might as well just have them send an email and plug it into an SQL template that you saved from the last request. If it's repetitive and frequent, then I think it makes sense to build a simple UI and let them deal with it.
It could also depend on what you like. You mention wanting to build system over changing business logic. So maybe you would like building the system for them to make thier own changes vs making updates yourself.
I do feel you om the business logic stuff. I'm currently dealing with a problem because of the business requests. They commingled business display content and system data in one field, then the other team decided they would change that field content per the business request without consulting with downstream systems. Not to mention they aren't properly following json format so we have to do some escaping/parsing before running the message through a real parser... it's so frustrating. And of course the pressure is on me to fix it, and my suggestion to roll back that change the broke multiple systems was a no-go. Apparently form is more important than function.
As an example, maybe they want to change a cutoff from $100 to $50. You can provide them a standard query for modifying this field. Then they can change the cutoff value as needed. You could keep the SQL to yourself and just plug the number in that they gave you and run it yourself. Of course if you code it as an SP then it's fairly trivial to stand up a basic service and UI in front of it for them too.