A car with 12 months MoT will be more desirable to a buyer than one with six months or fewer, but how much value that would add to your vehicle depends on the inherent value of the vehicle in the first place. Given that your car is likely worth around £10,000, 12 months MoT would only be worth a fraction of the selling price. However, if you are confident that it will pass without requiring additional repairs, the cost of an MoT would be a small price to pay for a quicker sale.