Here's a simple way to decide:

• What's the damage? Small hole or seam issue? Repair. Fading or stretching? Replace. Stains or holes in the middle? Retire.
• What's the GSM? If it's high and you're always hot, replace with a lower GSM. If it's low and you want more structure, replace with a higher GSM.
• How often do you wear it? If it's a favorite, invest in repair. If it's been months since you wore it, maybe it's time to retire.