I was at Spa for WEC this weekend and experienced the new Eau Rouge stand and other changes. Here's some observations (with an emphasis on photography, which is my thing!):
The whole of the area opposite the endurance pits remains a building site, though you can walk over it and there is some nice viewing high up on the bank, although you're sitting/standing on a huge pile of rubble!
The Eau Rouge stand is awesome. It offers possibly the best view in motorsport, over the whole circuit and with unimpeded view of the straight, Radillon and Eau Rouge. Access was free all weekend.
The stand is VERY steep and it is all bench seats so you need a head for heights. I lack that so I didn't go up. However, at the front/bottom of the stand there is a railing with the first row of seats set back and a little up. That railing was end-to-end photographers. I got my spot 2 hours before the start and spent much of that protecting my space with sharp elbows!
From the end of the stand nearest Eau Rouge there is a clear view of the straight and the curve. However, while it is awesome viewing it's actually less interesting photography-wise than the old fence cut-outs because it is harder to capture the elevation changes or get interesting angles.
The other end of the stand provides long and possibly more interesting shots of the cars cresting Eau Rouge. Less dramatic viewing, more compelling pictures.
There are more fences and higher barriers around Les Combes and Malmedy, meaning the loss of a few shots. It's no longer possible to get the head-on of the cars rounding Malmedy shooting through the fence next to the old caravans.
Around Bruxelles little has changed viewing-wise. You can still shoot through the big gap that the TV cameras use. The area on the outside of the track on the run down to Double Gauche is clearly going to be a viewing area but it's still a building site now. There is also a lot of work being done around Campus.
Was there always two tunnels under Eau Rouge to the paddocks? I don't recall. Anyway there's two now, one of which looks new! Nothing was different in the Paddock area at all.
I don't know if it's currently possible to walk all the way round La Source. I suspect the bank where you could get cheeky high shots of the corner is now blocked off. But by this point I was tired and wet and had 3000 photos so I bailed out
.