This is one of the most common dilemmas in collecting. Restoration can increase an item's beauty but sometimes destroys its value.

General rules I follow:
- Furniture: Light cleaning is fine, but don't refinish original surfaces
- Pottery/ceramics: Professional repair only, and disclose it
- Paintings: Leave cleaning to a conservator
- Silver: Polish is fine, but don't buff out patina on rare pieces

What's your philosophy? Have you ever restored something and regretted it — or been glad you left it alone?