Thanks!  I like this answer a lot since it suggests a nice/easy quantitative version of the question:

If your existing funding could be spent in an unconstrained fashion, what fraction of grant dollars would you spend significantly differently?

I think this scales between 0% (== fully aligned) and 100% (==totally different) research in a pretty straightforward way.

It only captures the "grant dollars" part of the original question (and not, e.g., deciding on a specialization in order to get a better chance at a tenure track position, or changing research in order to get a higher chance of getting past journal reviewers), but that's still pretty valuable.