I think some of the retro liveries were just... BETTER than a lot of the current, focus-grouped, artless abominations. By trying to please everyone, you wind up pleasing no one... just look at what The Gap went through with their attempted "new" logo! Branding isn't just about being totally inoffensive to anyone -- it's about conveying a certain character.
Just look back at the discussions of the CO
/UA livery. Almost everyone, regardless of preference, all pretty much agreed that the classic UA
"rainbow" livery was the best of them all. Heck, I'd even prefer the old golden CO
to the blandly corporate one they have now.
There's nothing stopping airlines from coming up with brilliant new designs that are even better... they just have to have the will to do so, take some risks, and let a real artist work, rather than a committee!
(one exception to my general assessment: US. They have had a history of some of the ugliest liveries in God's blue sky... their current one, by comparison, is clean and classy).