Steve,
I've only camped when I've been to a race there, but have done many track days at a Spa when I stay in a hotel, so others may have a better view for a race weekend.
The choice is to be in Spa or close to the track. I've stayed at Hotel Le Source - the hotel by the track, but it is soulless and probably booked out by race teams. My preference is in Spa itself because there are great bars and restaurants, but factor in the drive to the circuit in the morning. If I go with my wife I stay in the Raddison Blu right in the centre simply because it is right in the centre of town also there's a funicular to the baths at the top which is quite fun and a bit different to track work. See
http://www.thermesdespa.com/en/There's also the Casino in town too, if that takes your fancy - I've been but find all Casinos a bit of a home for the desperate.
Aricus