Firstly, who do you think would win in a battle, the Traveler or Q? Both are very powerful, and can manipulate time and space, and the traveler is more benevolent. Secondly, why was he never brought back for Voyager? He would have been a common sense guest star for that show, since he can travel long distances easily. They took advantage of this for the use of Q, but not for the traveler. Finally, why was there never any follow-up on him and Wesley Crusher? Is this something covered in Trek literature?
Q is more popular and recognizable than the Traveler, and therefore is more of a potential ratings grab. Wesley Crusher was featured in the A Time To novel miniseries from 2004 and will be returning in the TNG Cold Equations novel The Body Electric due out at the end of the month.
The Q. The Traveler showed signs of physical stress while attempting to get Enterprise home. And the crew were ordered to think happy thoughts about him to help him do this. The Q never seem to tire when using their powers, which seem to require no preparation or hocus pocus mumbo jumbo.
It also appears that The Traveler lives up to his moniker, with his primary power being the ability to travel great distances (and even between dimensions). No doubt it was simply the sheer amount of material and/or people he was having to move that was draining his abilities. The Q powers are much more varied.
Or then people are an important part of his propulsion system, and the greatest effort of all would be to move without any. Why does the Traveler enlist the help of the likes of Kosinski? Is it because he wants to get aboard Starfleet ships specifically? It's difficult to imagine why he would, as any warpship would serve. Is it because he wants clearance to modify the engines? But the modifications appear unnecessary, mere smoke and mirrors to hide the true nature of the Traveling. Probably he just likes company - that is, because he burns it for fuel! Timo Saloniemi
My impress is that the Traveler was there to help Kosinski look good, because that was important to Kosinski. The Traveler was being nice.