Enhanced conversions for leads - worth the implementation effort on a B2B account?

Yes it helps, and specifically because you import from a CRM - that is the case where it does the most work rather than the least. The mechanism: an offline conversion import has to be matched back to a click. Historically that match depended on you capturing and storing the click identifier at form submission and passing it back. Anything that broke that chain - a form that did not capture it, a salesperson creating the record by hand, a lead that came through a different route - was an unmatched conversion, which means it silently never counted. Enhanced conversions give the matching a second route using the hashed contact details you already hold. So the lift you are buying is not better measurement of what already matched; it is recovering the ones that did not. On measuring it: you can, roughly. Record your current match rate on offline imports before you start. That is the number that should move. If your match rate today is already high then the honest answer is that there is not much to recover and you should spend the goodwill elsewhere. Hope that helps.