VS does have codeshare agreements with a handful of *A carriers like CO and NZ, so you can collect miles that way.

I recently redeemed a chunk of miles through CO to fly to LHR one-way on AC and return on VS, to try out both in J. I think I enjoyed AC slightly better (though my VS seat was in the nose cone of the 747 which is always a winner), and VS met its well-earned reputation for awful on-board food.

There's nothing out there that compares to the Virgin Clubhouse at LHR. You should try it once just for that. You'll never want to go back to a MLL again (though even those are leagues better than anything we have in the States).