Again, this is one of the highly personal decisions. Knowing I would accumulate multiple Compostelas, Distance Certificates and Volunteer service certificates, I found an alternative method for preserving my memories.
While in Santiago, I went to a China Store / Oriental Bazaar and bought one A4 sized ring binder. I also purchased a supply of clear document protector pages, pre-punched to match the ring binder's pattern. If you do not live in the US, this is an easy enough thing to do locally, as we are perhaps the sole country that sticks to our old "letter-sized" and "legal-sized" document conventions.
In any event, I trim the A3 (larger) sized Distance Certificates to A4 size using a paper cutter I have. I do the same with the volunteer thank you certificates. Each certificate goes in its' own clear acetate document sleeve. The resulting "library" of certificates can fit on a bookshelf. I printed a label for the spine that simply says "Tom's Camino Certificates."
This simple and compact approach works for me. It might do for you too.
Tom