The game makes it fairly clear that the "man in the pipe" was one of the CLONES, based on the fact that he had a "2" tattoo, and left to attend the "Reunion."

Quote Originally Posted by G SpOtZ
]but how many of em were messed up like the guy in the slums?
All of them, really. Every CLONE encountered in the game can do little more than mumble "Sephiroth" or "Reunion" or some other phrase associated with the event.

Quote Originally Posted by Lord Magician
(1) In shinra corp. when he see's jenova in the lab.

(2) Temple of Ancients it takes over his mind so he helps out sephiroth

(3) Crater, gives black materia to sephiroth once again

(4) Mideel, he is mentally retarted.

There you go. Thoses are moments where jenova cell are affecting cloud or so I think.
The first incident was certainly induced by the direct presence of JENOVA. The second and third incidents involved the JENOVA cells, but also Cloud's own self-doubt and Sephiroth's direct manipulation. Cloud's incapacitation at Mideel had nothing to do with JENOVA cells; rather, he had floated through the Lifestream, absorbing the knowledge and wisdom there all at once. The doctor in Mideel made a point of mentioning that no ordinary individual could have even survived the journey.

Barret: So what about him? You know...... Cloud?

Doctor: I'll say it again, he's got Mako poisoning. I've never seen a case this
bad. An immerse amount of Mako-drenched knowledge was put into his brain all at
once...... No normal human could survived it...... It's a miracle he did!
As to the central question of the thread, I don't expect Cloud to have any sort of an extended lifespan due to the JENOVA therapy. He may naturally be long-lived or short-lived, but I can't see the JENOVA being of any benefit. Advent Children Spoilers and ConjectureIn one of the trailers, Vincent directly explains that Geostigma is basically the body overcompensating for the presence of JENOVA cells. This internal conflict between a Gaian's Spirit Energy and the JENOVA cells can lead to fatigue, open wounds, and even death. Based on this, his body seems to be trying to expunge the JENOVA, so, even if it did lead to longevity, it wouldn't be of help to Cloud.

Lucrecia's reaction to the JENOVA cells was clearly different than Cloud's, in any case. I'm hopeful that the Compilation, when complete, will clear up all these lingering questions concerning the effects of JENOVA cells.