A couple of things I will respond to (not because I disagree with what you've said):
Sorry, this has strayed waaaay off topic now!
I love Ludlow. Very nearly moved there once. But Ludlow is successful as a shopping centre because it pulls in people from a wide area, it pulls in tourists, and it's created a niche market for itself as a foodie capital. There will always be exceptions, but not every high street can be an exception.
You say that shops have been lost as a direct result of car use, and that's partially true (I think the pattern is much more complex though, and the desire for cheap prices requires large, out-of-town stores, which in turn require car use). But how does that assessment help? People still chose to abandon the high street. Social trends like that are caused by fundamental human behaviours that will never be changed by simply persuading people to do things differently. Price, comfort, convenience, choice.... these are the factors that influence where people shop, and the high street just can't compete. Especially in a world where people are increasingly expecting 24/7 opening.
You mention petrol and parking, but part of the reason people go to supermarkets is specifically to buy cheap(er) petrol. And whenever I visit a small town in my area, I get fleeced for parking (and I end up spending less time on the high street because requires advance guesswork over how long you'll be staying, so I've often ended up rushing back to the car before my ticket expires when I'd otherwise be staying for a coffee or lunch or a bit of impulse shopping).
You're absolutely correct. Many people are lamenting the death of the high street and would like to see something done. But the high street is dying because they didn't shop there. Nostalgia won't reverse that trend.
Much as I advocate the idea of shopping locally, I have to say that in my experience, this "added value" thing is a myth. All shops are run and staffed by people, and those people are just as prone to providing poor service and bad attitude as people everywhere. I've had some great experiences of local shops, but I've had just as many bad ones.
You say "let's start there", and in principle that's great. But the reality is that social trends aren't changed so easily. You and I might get on an extra bus a week, but the majority of people won't be forced out of their cars except by financial pressure or other coercive forces. That's just basic human nature.
As I mentioned a while back, I can't get to work by public transport. A couple of years ago, someone tried to organise a car share at work. This is a great idea in principle - significant savings (I must spend about £100/month on petrol for commuting) for very little sacrifice (picked up at home, taken straight to work). Nobody was interested. Not a single person. If you can't get people to sacrifice the use of their cars in such a scenario, you've got no chance of persuading them onto buses and trains unless there's a compelling pressure to motivate them.
As far as the high street goes, it's dead. Larger towns will fare better, as will tourist towns that can cater to a specialist market. But for smaller towns and villages, the game is already lost. I stayed in a small village on the north coast of Aberdeenshire in the spring. A couple of years ago, it had a baker, a pub, a post office, a village store, and another couple of shops. Now it has a pub, and even the pub's struggling. The village has no native industry left, and a once-bustling community is now just a dormitory village for Aberdeen's commuters. Towns fare better because they still provide jobs, but the trend is still urbanisation and centralised leisure, services and shopping.
Not keen on any of this, but hey!