Never purchased one, but sure have messed around with .css files a lot to try to get them to look the way I want them to. Like you, with very little satisfaction. There is such a wide spectrum of blog-type themes that there really isn't much need for personal tweaking to a high degree, in my opinion.

However, if you want to look different than anyone else, getting a sharply designed theme, and purchasing the entire rights... expensive, but makes real nice blog.