Another good reason to use a leader with braid is as a shock leader.
The braid has nearly zero stretch, so when a fish hits hard the leader gives you the stretch you need to avoid putting so much stress on the braided line even though with braid, the line breaking is usually a non issue.
As far as swivels and that go I prefer to use the least amount of hardware as possible, usually none.
I'll just tie a uni to uni from the braid to the leader and tie directly to the lure of choice. If some more action is desired I will sometimes go with a loop knot above the lure instead of the usual uni.
But if you want to use hardweare to make changing lures faster and without having to waste leader every time, I have seen a couple variations of the Quick Twist by Norton Lures (http://www.nortonlures.net/shop_by_department.php?DId=6
). I'm sure you could prob. find some variation of this.
Good luck, tight lines.