There's no such thing as a fixed value. The value of something is what a buyer is willing to pay for it. Since United's shares have been on the NYSE the market seems to have made a pretty conclusive view of what its worth. Albeit in a full float you would expect the share price to go up quite steeply, I am not sure they'd reach the level needed for a £4 billion valuation.
I struggle to see how you realise the value from the kind of things you're citing to support your valuation. Yes, United owns lots of stuff. However, how would a potential buyer realise value from that stuff? Is it really possible for a potential buyer to sell Old Trafford or Carrington? Hypothetically, yes. Any buyer is going to see the practical constraints in doing so though and price that into what they're willing to pay. 30 first teamers, again what's the value there and how do you realise it? I guess someone like Eric Bailly, having just signed a new deal, has a high book value. However, what's the realistic chance of realising that value? How many potential buyers are there who will give you max returns for an injury prone defender? We've been down this road before with Marcos Rojo. The quickest way to realise value from the first team would to get rid of your most saleable assets e.g. Bruno Fernandes. But that has a downside. In that getting rid of Bruno makes it less likely your team will win, therefore making it less likely sponsors will want to be associated with you at premium prices. You're still Man Utd, sponsors will still pay to be associated with you but if you're lacking your marquee names you put yourself on a downward trajectory for commercial revenue growth. At a cheaper price than £4 billion some investors will be okay with that but that's not what you're suggesting.
Ultimately we'll see if there is, as you said earlier, a 'mug' willing to pay £4 billion for United. However, I stick by what I said earlier: Anyone paying that must be either an idiot, a diehard red with money to burn or someone who has another agenda e.g. sportswashing.
