How do you choose between repairing a favourite backpack and replacing it for a little more?

The repair shop quoted $75 to replace my backpack's zip. A new backpack with the pockets I want would cost $120.

The old one is six years old, fits comfortably and has been on every commute since I bought it. The rest of it looks sound to me, but I don't know how long it would last after this repair. The shop expects to need two weeks; I could borrow a bag while it's there.

My partner says spending almost two-thirds of the new price on an old bag makes no sense. I don't think age alone makes it worthless, and I like the idea of continuing to use it. I also don't want 'repair rather than replace' to become a rule I obey without looking at the actual price.

Both options fit the money I've set aside. Would you pay for a familiar bag to keep going, take the extra $45 as a chance to replace it, or ask the repairer more before deciding? I can't tell whether I'm paying for usefulness, attachment, or a little of both.