I buy all my nice clothes at a local, very cheap thrift store and I must say that I do as little repurposing as possible. I never buy grungy clothes (like tshirts and shorts) since I can always get them from friends for free. Over the years, I've found that it's really hard to make major changes to garments like suits without making them look "changed". That said, if it's cheap enough I'll do it. Simpler garments like skirts and some shirts aren't such a challenge to "fix".
I just bought a 2 piece suit for $3.50 that had a too long skirt, and old buttons. I'll replace the buttons, shorten the skirt but that's it for structural changes. I really get angry when I think back to the days of buying $200 Tahari suits at Loehmanns. Okay I probably looked 10% better but it wasn't worth it then and definitely not now.
One thing I've seen in magazines is that clothes mostly stay the same but the accessories are different and are really the cute parts of the outfit. Just saw a fashion magazine today that had the cutest open toe white slingbacks with little ladybugs on the toe part. You could make little ladybugs or other cute designs and put them on plain slingbacks. I haven't tried it since I don't have the time these days but it seems like a really easy way to cute up an outfit. I'm always on the lookout for cute bags that I can gussy up. Also, cute cheap jewelry is a good way to set off an outfit.
oh yeah and i've sewn a lot in my time but I found that buying clothes from a really cheap source and doing minor alterations by hand means I could get rid of my sewing machine (I have a small living space) and spend less time sewing and the end product was actually cheaper than if I had sewn it myself (unless I was really lucky and got a deal on the fabric). your mileage my vary depending on where you live. I live around a lot of wasteful people so I get a lot of good stuff. Just bought a khaki skirt by ann taylor for $2. some cute slingbacks for $3.50 and a dress from target for $2.50 that i'll have to tailor to fit me a bit.