Did anyone say that mIRC versions are only bug fixes? Of course more features will be added.
Personally, I don't see why one version would be more of a favorite than any other version other than if a particular version gave you difficulties. There are some useful features in just about every new version of mIRC. Whether or not you need or want those features is up to you, but almost all new features are optional, so it doesn't hurt to have the newer version.
