As the creator of this thread, and someone who really liked Hernandez, I think we need to be careful in presuming it was a mistake to sell him because of his current form.
Ask yourself this: would you be happy with Hernandez as our long term, first choice striker? You can say 'But he's better than Rooney!', and that might be true at the moment.
But is he good enough to be a long term, first choice striker for a club with pretensions of winning the Premier League and Champions League - i.e. us? If the answer is 'no', then surely we should be aiming higher (and yes, that includes aiming higher than the current version of Rooney as well).
There are a few strikers around Europe who are capable of scoring regularly, without necessarily being good enough all round players for an elite side (what you gain in goals, you lose in other areas).
LvG didn't think he was up to it at the top level, and apparently Real Madrid didn't either, or they would've signed him. And we know he wasn't much interested in continuing to be a squad player. Hence the sale.
I'd love for him to still be here as part of the squad, but ultimately, he didn't want to be.
And I want us to sign someone in the bracket above come summer, so that our attack is spearheaded by someone who is world class or on the verge of it.