Last time there was a great NFS game was Hot Pursuit 2 on PS2. I didn't think Most Wanted was really that great, the Underground games were boring versions of fun games, and everything since Carbon has been on the decline. EA has Burnout as their arcade racing franchise and I don't think they're capable of doing a realistic racer, so I think it's time they let the NFS series die.
With GRID, Midnight Club, and Bizarre's new racer (unless the mario kart meets forza thing is a bit too crazy) all being good game and offering similar experiences, why would you go back to NFS other than the namesake?
Sacrifice Need for Speed for a new SSX