I've only seen the movies, not the animated series, but based on the movies (the first one being my favorite movie) i'd like a cartoon based on them. As to the original cast getting old a 'next generation' type thing wouldn't inherently stink, but i'd just have the cast voice the characters, who would look like they did in the movies- i.e the same way the simpsons characters voice actors are growing but the characters aren't.
Then again i suppose the franchise is getting dated... i only first saw the first movie in 2006 so i guess i'm behind the times a trifle... But it does have a fresh modern feel to it... I reckon an animated series based upon it could be successful... Perhaps the Ghostbusters could join forces with Kim Possible.