I've had plenty of wines, both young and old, that went from mediocre and uncompelling to excellent with air. And frankly, young Bordeaux in particular has a tendancy to be rather underwhelming at first, and then blossom.
The effect of breathing isn't limited to simply taking a wine's components and making them more expressive, rather it often actually does help them to resolve those components and acheive balance.
I think the only truism is that a wine that does not have the potetial to be good will not be made good by breathing (or by anything else for that matter).
Also, I think it's important to keep in mind that there is a difference between a wine that is good because it has potential versus a wine that is good because it is pleasurable to drink.
"The sun, with all those planets revolving about it and dependent on it, can still ripen a bunch of grapes as if it had nothing else to do"
(avatar: me next to the WIYN 3.5 meter telescope at Kitt Peak National Observatory)