Ok, I better understand why you have things implemented the way you have. If you decide to add the options mentioned, they could be a useful addition instead of what I asked for. After I add or correct the metadata in my files, I make them read-only to prevent inadvertent changes. So, a mode to store lyrics in the files themselves would not be useful for me. I don't need to prune the entire cache, I just wanted to prevent the empty files. What would be considered too large a cache?
Sometime I use playlists that only contain instrumental songs. It would be just as fast to disable the lyrics plug-in in this case, than enabling an option to not create text files. Those that mix file files with and without lyrics in the same playlist will have to find their own solutions for not wasting directory name space on intentional empty files.

I have been deleting the empty files to force re-querying for lyrics in case they may be found later, when the same files are played again. I understand why you don't want to trigger multiple online look-ups. I think it would be worth the resources used if lyrics are found later. I will stop deleting the empty files, if you think the re-querying will lead to crashes or other processing errors in WACUP. Wasting directory name space is worth it if it prevents WACUP processing errors, imo.
During a session, I have been adding the song titles above the start of the lyrics in the text files, after they finish playing. From time to time, there are errors in the lyrics found online that I have been correcting manually. During a session, I make notes of which files need corrections and these titles help me find these files faster in between sessions, when I make the corrections.
Reasonable people can always disagree on the best way to handle things. Whether I agree with your design decisions or not, I want you to know that I appreciate all you have done and continue to do that makes WACUP better than Winamp was, imo. I don't expect WACUP to do everything the way I would like things done. Expect for real bugs, I learn to work with the ways things are done in WACUP and the skins. In case of skins, I sometimes make small changes in some of their image and script files, when possible, to have them look and work more to my liking, for my personal use.