I haven't read the other posts in this topic, but the kind of coaster I'd most like to see in a family park is one that introduces children to some of the more adult like elements of rides.
As a perfect example of market research, my brother is about 13 years old and still too scared to go on any of the larger rides. What I think would encourage him to go onto bigger rides is if there was some small kiddie coaster, but with a tiny loop, or airtime hill, or something in there. If the theming was child friendly, i.e. bright and colourful instead of menacing like, for example Oblivion, I think more of the younger generation would become thrillseekers and consequently there would be more people visitng not just chessington, but parks with larger rides like thorpe.
The type of ride I have in mind would either be a sort of terrain style mine train, where at any one point you can only see a bit of a drop, but on the ride there are a few airtime hills and quite a large overall drop so that it gradually picks up speed; or a very small, 30ft or so 1 car looper, possibly pinfari (if they are still in business?) but basically a gentle drop into a pretty much forceless loop and then round a few turns and back into the station.
I appreciate that if a kid has a bad experience on a ride like this, he will think 'If that ride is scary, and that ride looks tame, then the scary rides must be really really scary.' which is why it would be essential to emphasize the fun theming and try to make it enjoyable instead of scary.
This idea will probably, unfortunately not ever get taken up but hey.
Oh, P.s. a very small enterprise ride, instead of the looper, if they make them in variable sizes, would be perfect for the job, and probably cheaper than a whoe coaster. It would have to be painted garishly though... hehehe...
P.p.s, after reading one of the above posts, I was reminded about launched coasters. This suggestion is not entirely serious, but how about a kiddie version of stealth with a 20ft, 45* sides, top hat and a 20mph in 5 secs launch? Just a little thing to show them that stealth isn't so bad...