I have started replacing EVERYTHING sooner. When I am starting to cut out a new quilt, I use a new rotary blade. When I start sewing on a project, I use a new needle.
Having invested (or more) in fabrics, then I can afford to spend another $5 on replacements. I still keep the 'used' blades and they are used for batting and/or paper. But I decided to make another investment in the project, knowing that it will be worth it in the mean time. Besides the cost of the fabric is the cost of my sanity trying to figure out why thinks don't seem right sometimes.
Since I started this, I actually have a more enjoyable time sewing. Go figure! I don't know why I didn't think of it first.
Oh - and I do the same with straight pins. If they don't want to go through or are bent, I toss them in a pop can.