When it comes to long vs short, let's cover the basics first:
-Shorter hair will make you look younger.
-Longer hair are great for taller guys to look more proportionate.
-Short hair are better for shorter guys as it will make the visually appear taller.
Personally, I would not say that longer hair are better than shorter (or vice versa) as it very much varies on case by case basis.
When it comes to your improved results ("vibe"), chances are it will boil down to a combination of subconcious changes (you feel better with longer hair -> feel more confident -> improved body language) and hairstyle emphasizing your best features, looking better with the rest of your style.
From my own experience, I was getting shitloads of compliments after cutting my hair short (from shoulder lenght), but have decided to grow it back because a) I know it will look better with overall style b) as somewhat of a wayward spirit, I feel better with longer hair.
Lastly, regarding the masculine vs feminine. There's a study that asked women about men's beards, masculinity and attractiveness. The results went something like that:
1) Clean shave -> Least masculine -> Average attractiveness for short term dating/sexual encounters
2) Stubble/Short beards -> Average masculinity -> Most attractive for short term dating/sexual encounters
3) Full beard -> Most masculine -> Least attractive for both short term sexual encounters and long term dating.
I would argue, that similar results would happen if we had a study on men's hair.
(more on this subject here: http://sexystyleforjoe.com/what-women-find-sexy/
It's possible to debate the quality of such studies (as no one is actually attaching detectors to vaginas and brains to monitor how horny women get), though my own experiences with changing looks goes to very similar conclusions.