I think 10 to 12 year olds are ready for top thrill rides and thats the problem, I know when I was 12 I was already doing the main rides in theme parks.
What would a 12 year old rather do, see animals or go on a coaster. I think most would choose a coaster.
I would love to see Chessington go for rides and attractions such as a really well themed drop tower with a good story just like Tower of Terror. Also something like Soarin.
The problem is always going to be the height limit that they can build to so a drop tower is really out of the question.
I dont know any thing about comics so I am of no use with that land.
I would also scrap the log flume, re-theme the area get rid of the dragon theme and make it more fun. Create a dinasor area it works in other parks, create a ride like Jarrsic Park (spelling) this works really well in the 2 Universal Parks and the whole family can enjoy it.
Scrap the current runaway mine train and get a proper one like at Disney. These are more thrilling and can be really well themed. They could build more wild west themed rides in the area, some good flat rides would go well like a Roundup.
I dont know if anyone else finds this but the area with the Bubble works just looks so dull, it needs brighter paint and happier area after all its a fun happy ride.
The Vampire area, what is happening with the ride staying or going? If its staying build a good ghost ride like the Haunted Mansion and just make the area more Vampire darker themed.
As for the zoo, well open it up more. Have more interaction with the animals, dont have full cages have open areas so people can look in. All they need to do is go to Colchester Zoo and they will see what can be done.
I also think they should look at what Flamingo Land have done, as that park now works for all ages.