One of mu businesses is Estate and Garage Sales. The Estate sales have taught me a lot about what is important to those left behind and your old cards will be tossed straight into he recycle bin.
The last home we did an estate sale at, the woman was 83 when she died. She had saved EVERY Christmas Card and EVERY Birthday card she had EVER received. I placed them all in a box for her daughter to go through and pick and choose. When the daughter opened the box and poked around, she said "toss it". This is exactly what every other client has said, but I still gather them for just in case.
If you enjoy your cards great keep them in a box, but do know they are more than likely not going to mean anything to any one else in the future.
Right now I have about 16 Birthday Cards hanging from my blinds. At the end of the month, I will throw them in the recycle bin,