I have a shelf for marching, holiday, marches (all labeled with grade levels), then a shelf each for grades 1-5, with PML pieces separated from Non-PML. Just have to leave space at the bottom to expand each category when you get new pieces. Keep a spreadsheet with titles/info and make a mail-merged label document that you can easily open and populate with new pieces to create a label for anything you buy new.
Re-organized the WHOLE thing like this a few years ago. It took a couple months of conference periods, but now the collection is user-friendly and takes 5 minutes to add a new piece in.