Does Restoring an Item Ruin its Value?

So I recently came into possession of a couple of items that need restoration, one of these is the considerably rare Talk N Action Gordon, I was wondering however, that if I were to fix these items and restore them to how they would have originally looked, would this affect the resale value? I plan on reselling some of them to start to make my own money and get a steady income by selling some for quite cheap prices, e.g TOMY Molly without tender for £3, let me know if it does affect the value or not, I would find the information very helpful!