Bringing Back Canceled Shows

It seems like the new thing to do on TV is to bring back tv shows that ended or were canceled, sometimes years ago.
Now being canceled or having a series finally doesn't mean its the end anymore. Shows from all over the history of TV can be brought back or revitalized.
They brought Family Guy back after years of cancellation.
They also brought back Futurama. But both shows were brought back pretty unchanged.
TV has also brought back 90210 with a new young cast, tried to bring back Melrose Place with a new young cast.
They also tried to bring back Night Rider, but it didn't work either.
Cougar Town was canceled, and then another network bought it, which happens sometimes.
Arrested Development, I heard, is new on Netflix.
They brought back Dallas with older cast and newer and younger cast members.
They are bringing back Boy Meets World, set years after the show ended with Corey and Topanga as parents of the daughter who would be the star.
There is apparently also talks of bringing Heroes back.
The BBC has done this too, with Inspector Lewis and the newer Doctor Who show.
There is probably a few I missed. Let me know if I missed any.
But I was curious what everyone thought about doing this. It used to be that when a show ended, or was canceled, you knew it was gone for good and never returning.

What shows would you want brought back from TV limbo/cancellation/being over?

For me personally, this might be a cheat, but I'd like to see Kids in the Hall brought back to TV with the original cast returning. Sure they are older now but they would still be funny and could do skits about current topics as well as random stuff like they used to.
I also wouldn't mind seeing Fresh Prince brought back. I know it would NEVER happen. But It would be nice to see Will and his Aunt, Uncle, and Cousins, get back together. See where they all are now. What happened to each of them.
And finally
I think they should remake the Waltons. The old Waltons show was about a family, 2-4 generations living under one roof during the Depression. They could remake the show with the same idea (could even be the same family generations later), during these hard economic times a family of 4 generations all live under the same roof. So you got the Grand Parents, the mother and father, the children, and the children's children (which would probably only be 1 or 2 of) living in the same house. Set in modern times, 2013, and could be as wholesome as the old show tried to be. Maybe it would be best for Hallmark or something.

 

These shows you guys want brought back, do you want them with the original cast? Like how Boy Meets World or Dallas is doing it? With the exact amount of time passing in their world that has passed in our world, to account for their age? So a show that has been off the air for over 5 or 8 years has been gone for that many years in their world?
Or would you want the show to be redone with a completely new cast? And would the show be a reboot like the Nolan Batman or Spider-man films were for their franchise or a continuation?

For example, if they brought back Fresh Prince I would want it to be the original cast but there would have to be a reason. Like Why would they all get back together after all this time.
But if they brought back the Waltons it would have to be an almost complete reboot. None of the old cast (since in our time they would all be dead or really old) with new actors and new stories.

Could there a downside to this idea of being able to bring back old canceled or ended shows?