In my opinion it's important, and I went ahead and got the 3 yr warrany.
Without the 3-Year AlienCare Toll-Free 24/7 Phone Support with Onsite Service, you may have to deal with a number of situations that severely limit the maintainability and upgradeability of your system. For instance, without the Alienware’s matchless warranty, if a part were to fail, you would need to contact the component vendor directly to replace your part. If the warranty for that specific part had expired, you would have to purchase the part from the vendor, which is expensive, and you will have to install the part yourself. Depending on how experienced you are with hardware installation, you may be forced to have the part installed by a third party. With the 3-Year AlienCare Toll-Free 24/7 Phone Support with Onsite Service, everything is taken care of for you.