Exactly. Intricate systems are pure noise for me, a simple MD file opened in a texteditor like Sublime is enough, or as you say just a simple taggable system or really just a bunch of files in folder - as long as you have great search you'll find stuff in no time and forget most as you should.

I personnaly just have a huge file with various notes, text, todos or whatever for each year divided into days, then i can just scroll up through days, or search to find out what i did and what day - some days have nothing, some have lots. Some topics / projects get their own file.