Hey,
again it depends on your use-case and how you use scripts. If you increment a counter, then the order of incrementing might not matter to you, so having a higher retry_on_conflict value is fine. The same applies if you have concurrent updates on different parts of the document, if you just want to make sure that all the updates are written.
However, if you overwrite fields and simply replace those values, then you might need to go back to your own application and let that application decide how to handle this. Maybe you can merge the data that has been written with the data that you want to write, maybe overwriting is ok.
For many cases, update API plus retry_on_conflict is good solution, for some it's a nogo, and thats how you evaluate if you want to use it or not.
Hope this helps, even though it is not a definite answer 
--Alex