The Right of First Refusal cast offered great advice on how to say no to appointment requests that aren't a valid use of your time.
Does anyone have a generic framework or response for turning down similar emails / tasks requests? So basically being asked to assist with a certain set of tasks or project(s) that aren't in scope and which I'd like to politely decline, what's a good way to respond with a "no" without being negatively impacted?

I try to do it as politely
I try to do it as politely (but firmly) as possible. And doing so in person seems to be the most effective.
My two cents
What I tend to do is think of someone I know in our organization who would have an interest in helping out or sharing their knowledge.
I usually find someone like that, let's call that person A. I then thank that person who approached me, B for the purpose of our discussion, and suggest they contact A which is far more capable at helping them with their needs.
It's a useful rule of thumb to aim for an A which is less senior than B.
However, at the end of the day I think you must balance things. Don't refer people too many times to any one person A and don't refer the same B person too many times to other people. From time to time it's inevitable that you take requests for your time that don't serve your day-to-day work for the sake of maintaining good contacts.