well, first of all, i'm an extract brewer also. i did the same thing as you for a long time. i just moved from one kit to the next. I knew that I could change things in the beers that I had made. Furthermore, I knew the kits that i brewed needed to be altered to fit the taste that i was REALLY looking for. So i went searching. Finally i found a book titled, Designing Great Beers by Ray Daniels. This book REALLY helped me to learn how to CRAFT a beer to fit within stylistic guidelines. So if i wanted to brew a Brown Ale it gave me the information to create my own beer within the confines of that style. This is a HUGE resourse. You need to understand the mechanics of brewing first though. However, through the beers that you have on tap and the ones you've bottled, it looks like you understand what you're doing. We change the beers because we're tweeking the beer until it fits the taste that we're looking for. How to tweek the beer will be inside that book. And, there's nothing wrong with letting a good thing rest and not messing with it. I'm just too curious to do that though.