Fantastic Four is definitely the priority, but thinking about it, Ghost Rider IS an important piece of the puzzle. Like the Fantastic Four, he also has a set of villains that're important for the Marvel Universe, especially if they're going to expand their supernatural universe starting with Dr. Strange. Ghost Rider would be an important cornerstone in that.
Much like how you have your Avengers "Holy Trinity" of Captain America, Iron Man, and Thor, the same holds true with their supernatural characters, with the three principal characters being Dr. Strange, Blade, and Ghost Rider. They have Strange, they recently got back Blade, and now they just need Ghost Rider.
And if that website predicting that Sony Pictures is going to go kaput in 2012 holds true, then it's possible that Marvel will be able to get Ghost Rider back a WHOLE lot sooner than five years. That would also allow them to get back Spider-Man. Admittedly, Spider-Man has the least to offer as it'd pretty much just be him, as none of the villains are any use anywhere else, but that's still a MAJOR benefit to Marvel, as well. Even if they keep Spider-Man self contained, we're still talking the property that'll likely be their biggest box office draw short of the Avengers. If they get Spider-Man back than Marvel Studios will be pretty much set, financially.