^I'd prefer not to see a third generation of Fett in the ST, and I don't think we're going to. Aside the main characters of the OT and their offspring, I don't think we'll be seeing a strong connection to any other characters in the entire saga (with the possible exception of Palpatine, although I'd prefer a fresh villain).
No return of Maul, no children of Dooku or Tarkin or Fett, none of that nonsense. It's too contrived and unimaginative. I'd even be disappointed if they give us something relating to Plagueis. He was just a sith who Palpatine deceitfully glorified for the sole purpose of influencing Anakin.
Now that I've had my short rant, I will add this: If they MUST bring back Palpatine, I hope they do so in a Voldemort type manner - an object or location that contains his soul, which he then uses to manipulate a good character (against their will/knowledge) in an attempt to return to the living. I would love to see a character that doesn't realize what they are doing and can't control it, while being utilized for evil, i.e., what Anakin's story should have been. If Anakin didn't constantly admit that he knew everything he was doing was wrong, the story of the prequels would be 75% better.
On the whole age issue, there is no doubt that the original cast will take somewhat of a backseat to the new younger cast members. That being said, we are most certainly going to be given some time for the older cast to hold the mantle. They were asked to get in shape (to a degree) for a reason, and although it would be silly to see them jumping around in the same manner as their old antics, that doesn't mean they wont see action. They will, and I trust Abrams fully in making it tasteful.