I have seen some boats rigged with a traveler near the stern, with the main sheet rigged to it. My mainsheet simply hooks to the boom midway, and down to the centerboard trunk. Is there an advantage to rigging the traveler?
Well, the short answer is, that there are advantages to both and if it works for you. . .
Center boom sheeting puts more load on the boom. However, if your boom is beefy enough, and the DS booms I've seem all seem pretty sturdy, that's not an issue.
When the sheet only pulls at the center, it has 1/2 the lever arm compared to stern sheeting. Therefore, you tend to see 3:1 or better purchase rigged in the mainsheet.
I have the end boom traveler with a simple 2:1 at the end and no extra purchase at the center. However, that's equivalent to a 5:1 at the center. The 2:1 at the end has twice the lever arm, so it compares to a 4:1 at the center. And, the one part that goes up to the boom in the center gets added, to make a total of 5:1. The traveler setup therefore uses fewer sheaves for the same mechanical advantage.
The other difference is that the traveler redirects the pull. When you pull on the boom, you adjust two things simultaneously: the angle of the boom in the horizontal and the angle in the vertical plane. The former gives your "sheeting angle" which ultimately define the angle of attack of the leading edge (luff) of your sail to the wind. The latter affects the leech tension, which in turn defines how much twist you have in your sail. By changing the direction of the pull you can control the relative contribution. (See also the "Basic Concepts and Techniques" thread).
You can achieve a similar effect by rigging a strong vang (which primarily affects leech tension).
Unless the current setup really doesn't work for you (or you are sailing competitively), I'd tend to leave this as you have it.