We're in a situation where our dashboard design is done by a very small number of people and dashboards can be audited before going live so we haven't had to be creative in this regard.
What I've found happening often is that widgets get copied from already audited dashboards and then adapted further, using the authorised formulas. But this is not immune to changes in the authorised formula or the data model. Once a widget is copied, it is its own thing.
Starred/Names formulas are I think the official way to share predefined formulas for metrics with other analysts. What you cannot do, however, is force people to use them, or stop defining other named formulas themselves. And indeed, if you change the datamodel or the formula, you still need to start over because I think old widgets/dashboards will keep using the old formula. I'd love to be wrong on that last one.
I think documentation here is important no matter what you do. Not only does that allow you to explain exactly what each metric calculates, it also lets you explain how that metric is arrived at and what the limitations are (for instance, filter-wise). People should want to be using the same, relatively simple, formulas because that means they can properly compare numbers.
