I don't want to take anything away from the Webalizer developers
webalizer is open source (GPL). You can either contribute to that cool project and send patches with your enhancements. (If they don't like the direction you take, you can still fork the project without taking anything away from them).
(Update: d'oh, just noticed that I confused webalizer with awstats. Both are open source, but webalizer is written in C, so perhaps not the answer you're looking for.)
BTW the other day I've seen a cool perl project that dumps Apache log files into a sqlite database. Depending on your goals that might help you, you could then do much of your analysis in SQL.