That's pretty much it, exactly.
As you may have already surmised, variables are globally-scoped by default, meaning all commands within the same session can access them, so if you want to have a "what did I last roll"-style command, all you need to do is retrieve that same variable value using the token you're already using in the "Write a Value to the Event Log" action.
If you also want to have access to the value you spoke initially to know which die you rolled, as you're doing in the "Say Something with Text-To-Speech" action, you'd need to store that in a variable as well.
The information retrieved by the "{CMDSEGMENT:}" token pertains to the command it's used in, so without storing it in a variable that value would not be accessible to other commands.