I don't think we need it but when you're talking about spending £40m+ you're looking at the area where you can improve the team the most. Kagawa, Rooney, Nani and van Persie are all worse than Ronaldo but none of them are worse to the extent that Cleverley/Anderson/Fletcher/Scholes/Giggs are worse than Fábregas, IMO. So I'd prefer to go for the midfielder because it'd improve our team more.
Either way I think it'd make us pretty unstoppable but that's not really the point. No-one's saying they wouldn't love to have Ronaldo. No-one's saying he wouldn't significantly improve our chance to win titles. They're just saying that a top class midfielder with an extra 5+ years left at his peak would do the same while getting rid of the one weak point in our side.
Getting as many of the world's best attacking players as possible in one team while ignoring everything else is the kind of thinking that saw the Galacticos underachieve. It's something the fans love to dream about but it's not quite as mouthwatering in practice once you get past the allures of the big names. We bring Ronaldo back here and he takes every free kick from within 50 yards, he scores about two a season and fecks up the rest, van Persie gets pissed off because he knows that a few of his in-swingers would've created more goals, the individualism in the team starts to grind away at that team mentality and work ethic that's been so crucial to our constant league success....