Are you still relatively close to London? Because your comment that "there's no vibrancy or creativity" sounds like something someone who lives round where I do would say, but then when you start talking to people, you realise that there is, but they don't perform or exhibit their work locally, as there's only a small audience, local artist exhibit in London, local musicians (who are any good) tend to be going into London for gigs. It's too close to London for touring companies for dance and music...
There will be interesting people doing interesting things, but while in London it's all made very easy for you to access them, you'll have to put effort in. Joining groups and clubs, being the sort of person who's 'involved' getting to know people better, you'll find out the other shit they're doing.
People who've lived their whole lives in our town do find it strange that when I lived in London, I knew the names of most, but not all the people who lived in the other flats in my building, had no idea of the name of the family across the road or in the neighbouring houses, or even would recognise them. That level of unfriendliness seems hideous to people who've never lived with it, and think London/big cities are 'cold', but it also does give you a freedom that it's unlikely that if you are behaving badly the people witnessing it would know who you were, even if you were only a 5 minute walk from your house. The fact that when you fuck up, everyone will know about it, does make people behave better and less interestingly.
I agree about being careful to over romanticise living in the city, are you sure hte norm of the area you used to live in would be better for your DCs to grow up like than the norm of where you live now? Do you really not want to raise your DCs to be "polite and decent" woman or men who "do the right thing"? Would you really rather they weren't?