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.

You could always scan them and store them electronically if you feel that some of these notes may be beneficial in the future.

I personally kept the notes that I felt would be beneficial. Classes related to my major and classes I had taken an interest in, I would keep. Notes I had that didn't seem useful long-term, I would recycle. I would use this same strategy for your notes for papers. If it could be useful for a future paper, keep it. Otherwise, dispose of it.

Scan whatever you may need again at some point so you have an electronic copy. If possible, OCR it so you can search.

This point has been made by others before, but here's what I would do going forward: try to take as many notes as possible directly in a big txt file, so you don't need to scan and OCR it afterwards. You can always search for relevant keywords in your txt later.

And you may want to browse through Personal Productivity, specifically its note-taking tag.