Pre-registration required for online account management

The functional spec for a current project states that users:

- can complete actions A, B and C via standard web form regardless if unregistered

- can complete actions A, B and C as well as X, Y and Z via standard web forms if they are registered, via a user account area.

The decision we're faced with is whether or not we ditch that first element, and insist that all users are registered to complete actions (which are based around account management).

Success of the project will be measured by the number of registered users we have at the end of a defined period.

Now, some of the "best practice" guidelines out there state that unnecessary registration is a bad thing, so to conform to them we need to make those actions available where they'd have the info in front of them.  On the other hand, how will they know about the other advantages (aside from text/banners) if we don't make them register?

I wondered what people's thoughts and views on this might be, and what approaches you may have adopted at some point in the past.

Many thank