Before I get going with this article it's important to be aware that although there are many weeks between Hungary and Spa only two of those are used for working. The rest of the interval gives the teams a much needed break. So, whilst I fully expect upgrades for just about everyone they'll be roughly of the order you'd expect between two races.
Early this season McLaren was very tasty and the Ferrari was not so much a prancing horse as a lame duck. However, in the break between fly-aways and Europe McLaren failed to make headway whereas Ferrari had a great upgrade which has allowed it to be competitive ever since.
At the point we leave I think McLaren is the best qualifying car and possibly the best car in the race. Ferrari are not the fastest in the race (behind McLaren and Red Bull, and perhaps Lotus) but are aided by Alonso driving very well. Red Bull seem to have lost their edge somewhat, and Lotus remain a little behind in qualifying but (at times) highly competitive in the races. Raikkonen is still a title contender at this stage.
Down the order, Sauber have not suddenly become rubbish. Their poor performance in the race was because they remain woeful in qualifying and because Hungary makes overtaking stupidly hard they couldn't put their better race pace into effect and were stuck in a procession to mediocrity. Williams seem to have patchy form, but some potential, although one shudders to think of Maldonado's car insurance premium.
So, that's where we are.
In upgrade terms we actually have advanced knowledge of a DRS plus system Lotus will be seeking to take to Spa. Basically, you get two smaller inlets flanking the big one (the hole in the car immediately above the driver's head) which channel air in an aerodynamically advantageous way, boosting straight line speed. They tested it at Hockenheim and Hungary and it's expected to be ready for Spa. More details are available here: http://www.bbc.co.uk/sport/0/formula1/19041743
Mercedes may be struggling somewhat with the car because of the DRS. Their system is a cut above everyone else's and channels air from the rear wing to the front wing, improving front end grip and improving performance when the system's active. However, this means there's a fundamental and significant divergence (more so than usual) between qualifying and race trim, and has made the car difficult to develop. There's more at the link: http://www.bbc.co.uk/sport/0/formula1/19064856
McLaren have also been working on a double DRS. They've said it isn't like the Lotus version, but I'd be surprised if it's akin to the Silver Arrow DRS, given their issues. It's also unclear whether or not it'll be used in racing this year: http://en.espnf1.com/mclaren/motorsport/story/86016.html
Another lower order team, Force India, are switching their developmental focus to 2013, which rather suggests they'll remain at the back of the midfield for the rest of this season: http://en.espnf1.com/f1/motorsport/story/86212.html
It's hard to assess how well or badly individual teams will develop, but we can at least look, briefly, at the drivers, who should remain more or less consistent with their first half performance. I'll run through them in points order.
Alonso - best driver of the year by a distance. Professionally positive even when his car was a dog, calm when collecting small points tallies and seized his opportunities when they came up. I expect nothing to change in this regard.
Webber - after Alonso the most consistent driver of the year. He's shown good pace in addition to this, and is matching his young team mate. However, I do wonder whether team orders may come into play from Red Bull (and whether Webber would accept them or not).
Vettel - has been driving well, but has also been under a little pressure after his ultra-dominant 2011 season. The petulant radio transmission to his engineer in Hungary betrayed a sense of frustration. He will be a contender, but is less mentally tough than some of his rivals (I think) right now. Team orders, should they occur, are likely to assist him. (If Webber follows them).
Hamilton - I think his performance this year has been underrated. He's driven well, he's suffered some bad luck that wasn't anything to do with him (most notably the Spanish pole that wasn't and McLaren's comedy pit stops) and is on a much more even keel than last year. With a recent and very helpful upgrade for the McLaren I think he might be second favourite after Alonso.
Raikkonen - the last man in a realistic position to contend for the title, which is impressive given he's only just returned. His raw pace is very solid, and he's been consistently scoring in the races. He's also the highest placed driver not to have won a race. Raikkonen's a dark horse.
The key, though, is the development war. If Ferrari win clearly or two of their rival teams do equally well then the 40 point gap and excellent reliability Alonso has shown will make him the favourite. Only if one of McLaren, Red Bull or Lotus can get a decisive advantage will that cease to be the case, in my view.
The next three races are Spa, Monza and Singapore. The first two are decent fast circuits, the last is a tedious street circuit procession. However, taken together they will hopefully provide a good pointer as to where the teams stand and where they're likely to finish.
Hard and medium tyres will be used for Spa and Monza, with the soft and supersoft planned for Singapore.
The Pirelli tyres of 2012 will not be altered, which is helpful: http://en.espnf1.com/f1/motorsport/story/86157.html
There has been some doubt raised over the future of the Nurburgring. It sounds as though it may now be safeguarded, but we'll have to wait and see. A quirk of the Nurburgring, where we are due to race next year, is that Vettel is not very quick there: http://en.espnf1.com/f1/motorsport/story/86068.html
Should the Nurburgring not return then it's thought that Hockenheim, this year's German circuit and the track that habitually alternated with the Nurburgring, will become the full-time German destination for F1.
During the break between Hungary and Spa I put a small sum on Raikkonen to finish top 3 at 3, with Betfair. My thinking is that Alonso has one place sewn up, which leaves 2 out of 3 top spots. There's just 8 points separating the drivers from Webber to Raikkonen, and two of them are near certain to get in the top 3 at the season's end. So, odds of 3 (or 2/1 in old money) seem reasonable.