It's a mistake to measure the success of a Moodle implementation by the amount of content on the site.
Just think about your own site for a moment.
Many Moodles have loads of resources placed there by staff back in the early days and never looked at since. You know the sort of thing, a member of staff receives some training, decides that Moodle is the best thing ever and spends the next few weeks uploading every PowerPoint they've ever written, pasting images onto every topic heading, setting up Forums, writing quizzes and setting assignments. Two months later they realize that what they've added isn't being used, not that it matters because they've moved on to a new enthusiasm. Even so, the course remains there and is held up as an example of good practice, despite the fact no one ever looks at it.
And that's just the tip of the iceberg. Think of the obsolete resources that staff can't bear to delete or archive, the duplicated materials, the imported materials someone's put on just in case it might be of use someday...
Although good content will make your site successful, the amount of content is not a measure of success.
So what is?
Well, the simplest measure is to see if those resources are being used. Moodle provides a number of ways of doing this, the simplest being the Participants block. Add this to a course, click on the link and you get a list of participants, sorted by most recent access. It's easy to see from this when students last logged onto the course. If it's a few weeks ago then you know that no matter how good your content is, it's not being viewed.
You can get a more detailed view of what's being viewed through the course participation reports and the site wide stats. All of these give you a quick overview of just how well your site is being used. A course may not look impressive, but it could be getting the traffic. It's the number of hits that counts. Are those resources being used?
There could be a number of reasons for all that traffic of course, including the fact that a member of staff is simply telling students to log on. This is not necessarily a bad thing: a text book is no less good a learning resource simply because students are instructed to use it.
Hit counts - whether driven by teachers, driven by interesting content, driven by whatever - are the measure of a successful Moodle implementation. Full stop.
... but that's not the full story, of course.
Because now you have to ask yourself this: is your Moodle effective?
And now you have to start looking at achievement...