As usual, the answer is....it depends. If, in your market, most garages are finished (insulation, drywall, textured, and painted) and yours isn't...would a buyer probably pay a little less? IN MY MARKET finished garages are nice but hard to put a value figure on. I tend to lump it in with such things as security systems, extra wiring, ceiling fans, upgraded appliances, etc.
From a personal stand point, I like the way they look and when we purchased our new home we had the garage interior finished and painted to match the interior of the house. Amazing how many comments we get on how nice the garage looks. Cost was about $1,000 more. As an added benefit, the extra wall insulation makes the garage warmer in the winter and cooler in the summer.