I forget to think if your goal is having item over +21. I see it isn't your goal. But I am gonna answear this question too.
If your goal is having item over +21, then I recommend downgrade item +19.
In future I will add comparisons between special upgrading tactics (for example: "Is good idea buying items +20 and try upp them?") including calculations of trying and golds needed.
I will also mathematicaly check, how good idea is to tolerate +19.
But now I need take a break from calculating. I will try finish this goal until Christmas event.
I wish you all the best luck in your Halloween upgrade event
If your goal is having item over +21, then I recommend downgrade item +19.
In future I will add comparisons between special upgrading tactics (for example: "Is good idea buying items +20 and try upp them?") including calculations of trying and golds needed.
I will also mathematicaly check, how good idea is to tolerate +19.
But now I need take a break from calculating. I will try finish this goal until Christmas event.
I wish you all the best luck in your Halloween upgrade event