Haven't read through everything but I think, that on the whole private education IS worth it, so long as you will still be able to afford a lifestyle similar to the majority of the other children (ie being able to pay for the extra ballet/mandarin/violin lesson at lunch time)
My children go to a private prep school and, while it isn't perfect (and no school is) I'm very happy with it, you get the sort of opportunities there I don't think you would get in a state school, dd1 who is in pp2/yr2 does ballet, french, latin, mandarin, swimming, piano, violin and gymnastics lessons weekly at school (some are extra cirricular some aren't) her brother has just started fencing, but that means I don't have to ferry them around from place to place, it saves us all time. They play sports on astroturf/netball pitches/tennis courts/ rugby pitches and swim in a full size pool.
By 13 all the year has a GCSE in french and some will have Latin too.
If you are considering private secondary education it helps to be at the feeder school/prep department where the children are taught to the entrance exam and will move up knowing lots of other children.
And while its not as important in the early years as your child grows up you know that the majority of parents at the school really care about their child's education - I know most parents at state school care deeply too but you can't deny you are more likely to find parents who don't.
Then again, my children are at a large and heavily oversubscribed school in a large city, in some smaller towns I guess schools won't have as many children to pick from and less money available to fund the facilities...
Whatever you choose I think your daughter will do well having a mummy who cares about her education so much!