We did New Years Eve in the Magic Kingdom for the Millenium. We spent the day park-hopping and entered the Millenium in the Magic Kingdom, less than an hour drive on I-4 from Sanford.
Fireworks at the Magic Kingdom
Cocoa Beach is about an hour and a half from Sanford, but only an hour east of Orlando. Cocoa is always on our itinerary, we enjoyed New Years Day at the beach and spent the night at the Marriott Courtyard Cocoa Beach.
Another idea is Treasure Island on the Gulf/Suncoast side, about 2-1/2 hours southwest of Sanford. I highly recommend the Residence Inn which is on the beach. The front desk is very knowledgeable and can tell you where the New Years action is.
Have a memorable time!