Here's some tips from a Belgian
I went to Spa in 1993, 1996, 1997, 2005, 2007 and 2008. The last two times are the most relevant to your trip, so I'll talk about that.
I bought bronze tickets on both occasions, because there are some great places you can stand and make pics that you don't need grandstand seats for. I usually go stand/sit at either the little straight in between the Bruxelles hairpin (Where Lewis Hamilton went off on the last GP) and the two fast left handers of Pouhon. There you can stand really close to the track, and you can see the cars flying accelerating out of the corner towards Pouhon.
You also have quite a good view at the Bus Stop. Be sure to come early to the track, as places there are gone fast. In 2008 I wanted to make a run for the podium, so I went to the La Source hairpin. There is a big gate at the large runoff on the exit of the corner. There is a big space underneath it. I crawled under it, and trough a hole in the fence, went on the track, and made a run for the podium! Be sure to hang around at the pitwall after the race, it might be worth it if the winning team decide to pose with their cars and trophies. Just climb on the pitwall opposite to the garages, and stand firm!
Minusses about the bronze tickets is that you don't see the Tv screens very well. I rented a Kangaroo Tv unit so I could follow the race and the support races. You also get very wet when it rains, and the grassy slopes become very muddy and slippery!
I bring a folding camping tripod seat, and a small stepup ladder in my pack, and a pair of plyers to cut a hole in the fence to make pics. Also, very important in Spa, an umbrella!!!
As for places to stay. There are many options. I stayed in the Radisson SAS hotel at Spa one time. Some drivers where staying there aswell, Alonso, Kubica, Massa, Raikkonen, Barrichello... You can hang around in the lobby if you have a room there, and meet some of the drivers.
For places to visit. Antwerp (my home town) and Brussels are nice, Ghent is very beautiful, and are all less then 2h from Spa/Liège. Germany is very close by aswell, Aachen, Cologne, Düsseldorf. And also: The Nurburgring!
Cheers, and enjoy!!