You need five days at Disneyland to avoid the busiest parts of the day. By having five days, you don't have to feel like you have to spend every minute of the day at the parks to get the most out of your trip. With a 5-day ticket, you can get to the parks early to beat the crowds. Then as the day goes on and the parks get busier, you can take a break.
Go back to your hotel for a nap or a swim, have a leisurely lunch at one of the themed restaurants in Downtown Disney or even hit the beach! Then, come back at night for World of Color or the fireworks.
Extending to five days can make your Disneyland vacation relaxing. Well, maybe not quite relaxing, but at the very least, super enjoyable and not rushed. Does a laid back Disneyland vacation sound good to you? Then five days is your golden answer to "How many days do I need at Disneyland?"