The goal of training is to gather as much fitness as possible into your training account. Small deposits made daily will add up. You need a combination of shorter more intense efforts and longer steady efforts. Running alone can create muscular imbalance and having a plan that keeps you strong and agile is key. 

Do you want to be a big spender on race day? Then make sure you have a good investment strategy. A solid training program will keep you focused and make sure that all energy systems are on board to help you pay the bill on race day. There are no get-rich-quick schemes. You need to put in the time, and plan long runs strategically to avoid compromising consistent training.