I'm basing it on winning the CL and/or league regularly instead of completely missing out on CL and coming outside top 4 regularly. Winning the CL is worth ~£70m. Winning the PL vs coming outside of CL places is worth about £10m. Even just doing well in the CL and coming in the top few of the PL is worth ~£30-40m vs not.
And yes, considering how many times City have won the PL and done well in the CL over the past decade, a well run United would very much have expected to do the same or better.
Why not? We have the largest fan base in the world. Brands want to associate themselves with successful enterprises.
We also currently have ~£1bn in debt and need to inject another ~1bn into the club to modernise the facilities.
So yes, I do think that all these things combined would have our valuation at probably double what it currently is. I'm not talking Glazers valuation, I am talking the valuation that is made by third parties with no vested interest in selling/buying the club.