Disposing of old written notes
It may help you to understand that much of the value of those notes has been the very act of writing them.  As such, you may find that you have less compunction against throwing them out.  

Personally, I maintain an "aging pile" for notes, in which I keep them until they stop feeling relevant.  For some things, that's a week; for others it was a box in my closet and a decade.  You can also remove the physical clutter aspect by scanning and archiving in something with cloud storage: you'll be trading physical clutter for electronic clutter, but I at least find that electronic clutter is much easier to ignore.