Such a difference! Well worth the money. I used to be like you in that I had lots of really great hand-me-downs from my friends and mother-in-law. Unfortunately, they weren't wonderful on me because the fit wasn't right for me. My outfits might have been made up of clothes that had beautiful, expensive fabrics and nice cuts but I looked frumpy. I didn't see it because I was seduced by the fact that they were such a good deal. My confidence and style quotient have increased exponentially since I figured out the value of good fit.
I hope I don't offend, but I see a similar transition in your outfits. The pre-alteration outfits were passable but not wow. Something about them seemed just a little off. Post alteration they are wonderful (especially the polka dot skirt and the patterned skirt), so much more flattering, and look much more current.
Free and cheap can have a price. If you're getting things that don't work for you, your style quotient pays for it. The nice thing though is once you've figured out the fit secret, you can train your eye so that you can go back and find those thrifty finds that really do look like a million bucks.