This has turned into some what of a long post. So tl;dr version first. Roughly 9000 to 10k characters, so give me 9-10 posts before responding.

Tl:dr
We've been running a closed circuit PvP between linkshell members.
Its a great training tool for newer members.
Its takes the pressure and frustration out of pug groups.
It provides insta ques for r30 and above members.
It provides your people with alternative rule sets to play with.
It mixes players, it makes higher ranks group with lower ranks.
It mixes players, each tends to learn specfic tendicies of other members.
It mixes players, getting more members used to one another, getting your group "frontlines ready*
It is flatout the best way to introduce healers and blms to PvP.
You can practice tactics, and request the other team to employ tactics you wish to learn to counter.