As a business, if they had no debt, they'd be an excellent investment on one level. Producing £90m cash a year probably values them at over £1bn, plus they're a global brand.
However they're loaded with £500m of debt and the Glazers' other financial issues mean that they would probably need a lot more to sell than the business is actually worth. Effectively they're in negative equity I believe.
Plus there's the uncertainty over Baconface, who is surely in his last season now, and what that would mean to their future income stream if a new manager couldn't sustain his level of success.
So you'd have to pay a premium price for the business plus you'd need the money to finance player purchases and pay off the bonds. I guess anyone who has something like £2bn burning a hole in their pocket might well be queuing up.