I ride DC to NC round trip 3-4 times a year. The Silver Star has pretty poor on-time performance records, but a lot of the delays are south of NC. You can pull the most recent week's data from Amtrak's website; it looks like pulling into Cary, the train varied between about 10 minutes early and about 40 minutes late. My general approach to Amtrak is that if I arrive within an hour of schedule, it counts as on-time. Set your expectations appropriately and you'll be much less stressed.
Amtrak currently has a "book two people into a roomette for the price of one" sale going; taking a roomette from DC to NC seems sort of silly to me, but if you've never done it before and want a new experience, you could look at the prices for that. Coach for two will be cheaper, though. That's the only promo I know of currently.
Amtrak points expire after 36 months of no activity, so you've got a while to plan your next trip.