I'm sure that Vettel has reached the point long ago where he deems himself financially sound, snags.
I doubt at this stage in his career he's doing it for filthy luchre. He needs a new challenge as he looks a little jaded and as the pundits say, every champion wants a spell at Ferrari at some point to see what they can do with the prancing horse.
As for the car, I'll reserve judgement. The FIA make changes every year and the best chassis/engine combination seems to change hands every 2 years or so of late. Remember when the Red Bulls were unsurpassed? It's currently the Silver Arrows, next season: Who knows? Rumours abound too that McLaren may be next season's hot ticket.
However it all pans out, it'll be exciting.