As a parent of children who were pupils at Vinehall and others who still are there, I feel I must sing their praises. I am not sure where you heard they were closing classes, but the school is thriving and by such a large margin is the best around.
Academically, Vinehall is streets ahead of Battle Abbey, Claremont (who drive everyone to distraction with their saturation of ghastly car-salesman style adverts), and Buckswood. As a parent I know the pupils from Vinehall go to a huge number of different senior schools, probably more than any other prep in the East Sussex / Kent area. In my elder child's year pupils went to Tonbridge, Eastbourne, King's Canterbury, Eton, Benenden, Winchester, Battle Abbey Senior, Lancing, St Leonard's Mayfield and Cranbrook to name a few. I guess it is all about receiving the right advice for each child to find a school where they will be happy and successful. Vinehall just seems to get this right, as there is no pressure from the staff for them to go to any one senior school. Unlike some others, especially Claremont where I am aware from other parents there is huge pressure to go on to their senior school.
Facilities are possibly too good - they simply have everything any child could ever need, but this is perhaps also a strength of the school as it allows every child, however different they may be, to excel at something in their time there.
As for particular non-academic strengths, sport - yes, music - absolutely, drama is fabulous and art is on the up.
So what are the downsides? Well, possibly the fees could be lower, but I do believe you get what you pay for, and as parents we have got so much from them I would gladly (almost) pay it again.
I realise I now sound like I must work there! Sometimes when you have something so good, you need to tell others!
My advice would be to go and have a look round. That is what we did first, and having looked at one or two others, we would never choose another prep school.