I've really got to agree with you here, I think the way TNA had Jeff re-debut with the company was pretty lame. I mean, come on...they're putting him in a program with Homicide? ...that's going to be SUPER-lame.
I hadn't really thought about Hardy in TNA the way that you had. You bring up a great point: with Jeff in the x-division, he really won't stand out NEARLY as much as he did in the WWE. He really wouldn't fit in the main-event right away either, at least not where the main-event is now.
If it was up to me, I would have had him feuding with Eric Young for the Global-Championship upon his arrival. Not only would this elevate EY's status as a super-heel, but also get Jeff's new TNA-credibility back on track for his eventual rise to the main-event (if they're smart).
Jacob (my eight-year-old) once told me that he didn't like TNA because "it doesn't have a lot of guys I know". Jeff Hardy is far-and-away his FAVORITE wrestler. Now that TNA has his favorite guy, he's going to start watching it...but my theory is that he'll quickly get bored with Impact (and Hardy too), unless they put Jeff in a storyline involving some type of championship. Jake didn't really start liking Jeff as much as he does now until he got put in the title-hunt on Smackdown.
Just my two-cents, I don't really see TNA's benefit in signing Jeff unless they put him in a storyline with a "credible" wrestler. A feud with Homicide is NOT going to excite the kiddies....against EY? Fantastic....maybe the Homicide feud will lead to a possible feud with World Elite, and eventually a run with the Global Title. Hopefully that's what's in store, because I really don't see the current plans unfolding in Jeff's (or TNA's) favor.