Can't help but feel a lot of people are letting sentimentality cloud their better judgement on this debate.
I keep hearing a lot of fans say "he's better than what we have now" as the main reason to bring him back. Aye he is, but the only reason for that is because what we have now is utter garbage. Is he good enough to get in Liverpool, Spurs, Chelsea or Arsenal's sides, even in the second striker role to back up a main goalscorer? Absolutely not. Because those teams don't have utter dirge like Kone, Valencia and Niasse on their books, they went ahead and actually signed some decent back up options which we never. Rooney isn't even a 15 goal a season striker anymore and that's the reason United want rid.
He will never be a world-class sitting, creative midfielder and we already have an older player in that role anyway in Barry, who has played in that position his entire career and knows his job to a tee. I know which I'd prefer to have in the team.
Play him as a number 10? We could do with signing a player for that role but there's far better, younger players we can get rather than a 30-something former striker. Now that we finally have some real dosh we shouldn't be resorting to taking in unwanted cast-offs from other clubs and hoping we can get something out of them like we did for years under Moyes, we're not plucky little Everton who always have to make do anymore.
Bottom line of the point I'm making is we should be looking to sign players who have their best years ahead of them, not ones whose best years have gone. If it were any other player no one would want him, its just because it's Rooney and the emotional side of it. I think it would send a far bigger message of ambition if we left him be and showed the world we're not interested in bringing back an older player for sentimental reasons, we want only in-their-prime players because we want to be the best ASAP.