Bayern Munich are a great example. A team that was run far too prudently as they were quite successful because of their size. Three years ago they seemed to make a clear decision: lets spend big where necessary to be the best, rather than be frugal and just be quite successful. Since then they've spent around £150m on Gotze, Alcantara, Martinez, Shaquiri, Mandzukic, Neuer and Boatang (around £40m per season net).
Now I think we'd all agree that they are one of the best 2-3 teams in the World.
United have a really good team and in recent years have concentrated on buying in (potentially) top quality young players (Smalling, Jones, De Gea, Hernandez, Zaha, Powell) along with a few solid squad players in Fellaini, Young and Kagawa. What we haven't done is what teams that aren't run by money men go out and do (or what we did a decade ago) - spend that little bit more on a World Class player or 2 to add that little bit extra (RVP aside as his contract situation meant he became affordable).
I guess my overall point is: why be "merely" successful when you can be truly exceptional? The likes of Barcelona, Bayern and Madrid don't settle for being "just" successful, although obviously it isn't financially prudent from an accountants point of view.