2 things: in keeping the veterans in touch, a club always gains something from their experience - advice from one of the legends has great value particularly for younger players. But particularly keeping a specific generation close, there's an extra gain, mainly for clubs like ours, looking to establish themselves as top clubs.
It has to do with the legacy: the Henrys, Lehmans, Pires-Dixon-Adams-Keowns are not looking to immortalize their names alone - they'd settle with the invincibles legacy for that. They look for the continuity, the next generation, they look to enhance the club itself - and I think they have that potential. I know this may sound thin to some, but I think it's real.
It'll be a bit cheap to summon the Henry example (as one can easily say: ok, coz he's Henry. Which is true in itself). But it does the work nicely from several angles: Titi had said many times only after leaving he became a fan (which I'm sure sounded strange to not just me: he was obviously a fan before, too? he certainly looked like on) - and I think he really meant he found a new level of being connected to the club, and with it looking for that invincible story being more than a one off, but something that helped place us on the top shelf for good.
Much to say about it actually, but I'll resist the temptation for now. Not a bad idea for a thread, if somebody feels like starting one.