Talk about the price of everything and the value of nothing. Economics is not a God! Quality of life is at least as important and will become more so in a post-industrial society.
Quality of life is why we need to embrace redevelopment. The existing buildings are crap.
Our current policy of not allowing redevelopment means there's essentially a cap on the number of rentable sq ft available. You can't add much more sq ft without knocking down a building and replacing it with a taller and bigger one. Permitted development might allow some side return and dormer extensions but it doesn't solve the problem.
Living standards are increasing and so people expect more sq ft per person. If there is a cap on the rentable sq ft available, then all you get is:
1. Fewer people get to live in the area and benefit from local facilities.
2. The same or more people get to live in the area but by sacrificing how much space they have per person.
In many areas of London we are seeing 2 happen today. We are essentially reinventing slums and single ends in the form of HMOs. Young people can't afford to live in London without sharing with multiple other people. Landlords can make a lot of money splitting up properties into smaller units for those who are really desperate.
Central London is one of the areas most suited to building new properties. Nowhere else in the country provides the same connectivity for people to live without ever needing to own or drive a car. The city already has a dense public transport network, and adding more demand is a brilliant way to make the economic case for capacity improvements. The more people who live around Euston the more you can justify building new Tube and Crossrail lines through it, with the added bonus of connectivity with other rail services at the mainline station.
Redevelopment doesn't mean building crap new buildings. It would be totally fine for the new buildings to be clad in nice materials and with nice shapes for windows and so on. They could be made to be clad in Regency-style stucco or traditional London brick and sash windows. The interiors could be made with faux fireplaces and cornicing. The point is that the existing buildings have to be demolished to provide more room, and that means existing owner-occupiers will see a bit of disruption and some sightlines will be lost.
If there are specific heritage buildings to be kept, then the new density around them helps a lot with making the financial case to retain and improve them. If there are more people living around and they have more money left over after paying their rent, then they'll be more likely to go to theatres and other valuable public venues. Maybe the new developments could include brand new theatres and public venues like pubs? Or the old ones could be kept around and improved.