I would argue the distro is mature, maybe the services (forum, wiki aso.) are not yet but can be improved with the help of feedbacks and suggestions.
Before this awesome storm of newcomers basically all the old users attending the forum knew how to Search the forum, download nightly builds from abf, which are the most important topics to follow, etc. because we did grow up together.
As for contributing with testing, until now we have mainly relied on internal testers, developers of course, and some aficionados common users who provide positive feedbacks and/or reporting malfunctioning when they upgrade system, install new packages, etc.
We are resurrecting the QA category with the purpose to make better profitable use of it.
The team will make a new post or review the one already in place soon and try to answer to all your questions on how to contribute with testing.
Also we are publishing more informations ([1] and not only) as soon as we realize it’s necessary to know for newcomers.
The point is to make them as simple as possible although easily understandable.
We’d like very much to make all perfect, but as you know nothing/nobody is perfect.
Working on it 
Those of us that have figured things out need to help with pionting people in the right direction
Yes, that would be very helpful. So far the excellent @ben79, some developers with quick incursions at the forum to better clarify some more technical bits, and me have been sufficient to manage the forum however that may well be not enough nowadays 
Thank you.