What do I do with all this stuff?

I want to be respectful of my mom and of the things that meant so much to her, but thinking ahead to the day when I will try to reclaim my home. There are so many things she's collected that meant the world to her...cookware, dishes, art, textiles, and a mountain of research of research compiled for her writing and unnecessarily long record-keeping of receipts and statements and projects she'd like to get around to someday (but never will). It's been quite crowded as it is with her living here, as there isn't much in the way of storage in my house, and I refuse to pay monthly $200 or more to store things I don't need and/or don't want. I care about how she feels, but so many of these things she clings to as they are a part of her identity. Some would be worth money, others are merely sentimental. But I simply cannot store everything that was hers and have room for the things that are important to me. Eventually I will have to downsize. My children don't want these things...the society we live in is SO different than that scarcity our parents lived through. I'd like to start culling things soon, as the clutter makes it difficult to clean her room and it's becoming a trip hazard, but it's very distressing to mom as she says "I need to go through that stuff, so don't go throwing anything away yet!" She doesn't have the ambition or energy to go through it herself, yet I feel the mess is as depressing to her as it is to me...reminds her of a thousand and one things she hasn't completed.