This is looking good! Simple just like my xanChat used to be back in the day.
Over the years though i've added stuff along the way. So I totally know what you are going through. Keep up the good work! Keep practicing and reviewing other code, it definitely helps in learning! Remember to keep things the way you like them. Suggestions are nice but the key is to stick to what you need and that it works for you.
After reviewing the code, it's simple and clean. But a few things I'd like to point out
1) You have reference to LibStub("LibAboutPanel") but you aren't actually using the Library. The current code expects that some other addon has it loaded. If you aren't too keen in having an About panel, I don't think that code is necessary. Otherwise, that library is actually extremely tiny and should be okay to add to your addon using LibStub.
2) Be careful when tampering with Alpha layers or Backgrounds on the Chat Windows. It causes Taint errors like crazy. This is because some elements of the Chat Windows are tied to the new Edit Mode option of the Retail servers. Be warned there are some functions and elements of the Chat Frames that will cause taint issues and are not so easy to pinpoint! It was a pain to resolve these on my addon xanChat.
Otherwise this is an extremely simplistic and clean addon. Minimalistic and honestly that's a good thing. Nice work!
P.S: I also noticed in the screenshot you are using my addon BagSync.